# What if our galaxy didn't have a SMBH?

From my understanding, it is believed that almost every big galaxy and especially spiral galaxies have supermassive black holes (SMBH's) at the center. Also, from what I've read, a SMBH isn't required for a galaxy to exist since and in layman's terms, the matter inside a galaxy such it gas clouds and formation of stars will keep it gravitational-ly in check.

If I am right or even wrong, then would there be significant difference if our galaxy did not have a SMBH at the center? Significant enough for noticeable differences even here on Earth?

The supermassive black hole (SMBH) in the center of the Milky Way (MW) - called Sgr A* [Sagittarius A-star] - has no direct impact on our galaxy. Its mass is only a few million Solar masses, and if you remove it$^dagger$, it will only affect the most central stars, which would suddenly continue in straight paths out through the MW. These stars would almost surely not hit any other stars or something like that (since stars are really, really far apart), but some of them have velocities high enough that they may escape the MW.

If Sgr A* weren't there to begin with, things might look a little different. There seems to be a relation between the mass of a galaxy's SMBH and the velocity dispersion of the stars in its central bulge; the so-called M-sigma relation. so MW without Sgr A* would mean a more ordered center. Our Solar system is located in the disk, far from the center, and their is evidence that SMBHs have little impact on the disk (Gebhardt et al. 2001). However, in their early phase (as an active galactic nucleus), their extreme luminosities cause galactic superwinds which blow out gas and may quench star formation (Tombesi et al. 2015).

$^{^dagger}$Removing Milky Way's SMBH is left as an exercise for the reader.

## What happened to this galaxy’s dark matter?

Back in 2018, astronomers used Hubble to observe a relatively nearby galaxy and found it presented a baffling mystery: It appeared to have little or no dark matter.

This was so weird they decided to follow up to make sure their results made sense. So they took more Hubble observations — a lot more — and the mystery only deepened. It appears to have even less dark matter than they originally thought.

This is unexpected, and bizarre. Why doesn’t this galaxy have a feature pretty much every other galaxy has?

The ultra-diffuse dwarf galaxy NGC 1052-DF2, seen here using Hubble, apparently has little or no dark matter. It’s not clear how this happened. Credit: NASA, ESA, STScI, Zili Shen (Yale), Pieter van Dokkum (Yale), Shany Danieli (IAS) Image processing: Alyssa Pagan (STScI)

Okay, to start, the galaxy is called NGC 1052-DF2 (let’s call it DF2 for short) and was discovered in 2000. It lies near the much larger and brighter elliptical galaxy NGC 1052 in the sky, and was found to be physically close to it, too.

DF2 is faint, and very diffuse (so diffuse, in fact, that you can see background galaxies right through it). Given the initial distance measured to be around 65 million light years from us, that makes it a dwarf galaxy but a biggish one, about 20,000 light years across.

The weirdness started when some short Hubble observations showed it has several globular clusters around it, huge collections of hundreds of thousands of stars. These clusters orbit galaxies, and how fast they orbit depends on the mass of the galaxy more mass means more gravity and faster orbits.

The astronomers measured the velocities of the clusters using the immense Keck telescope, and found a mass for DF2 of about 200 million times the mass of the Sun, and no more than about 300.

Here’s where it gets truly weird: They also looked at the visible light coming from the galaxy. Assuming it all comes from stars (a very good assumption) they also get a mass of… 200 million times the Sun.

BUT. We know that galaxies are surrounded by a halo of invisible stuff we call dark matter, and that this generally outmasses the visible stuff by a factor of five or so. That’s not the case for DF2. Assuming they got everything right, the total mass of the galaxy is about or not much more than the visible mass. That means it has very little or no dark matter.

And that’s very weird indeed.

As it happens, there’s an out: If they got the distance wrong, this situation can be fixed. If it’s a lot closer to us than 65 million light years, say around 42 million light years, then the galaxy isn’t as bright as we think, the visible mass drops but the total doesn’t, and that means it does have a dark matter halo. In fact, using the same Hubble data, some other astronomers did calculate a much closer distance from the galaxy. So who’s right?

To find out, they got more Hubble observations. The first time they observed the galaxy they got a 4,500 second exposure. This time, though, they went deep, getting a total of nearly 90,000 seconds, almost 25 hours, 20 times the first exposure.

The galaxy NGC 1052-DF2 (left) with a close-up showing individual stars in it, including red giants which are used to get its distance. Credit: NASA, ESA, STScI, Zili Shen (Yale), Pieter van Dokkum (Yale), Shany Danieli (IAS) Image processing: Alyssa Pagan (STScI)

The images showed much fainter stars, including a lot of stars called red giants. These are stars like the Sun but nearing the ends of their lives. When they run out of hydrogen fuel in their cores they swell up and cool off. Eventually they start to fuse helium, which makes them shrink a bit and heat up. The beauty of this is that the brightness of these stars are all the same when they switch to helium fusion, making them great distance indicators. We know how bright they really are when this happens, so by measuring their apparent brightness the distance to the stars (and the galaxy they’re in) can be found.

Here’s the really fun bit: They looked at 5,400 red giants in the galaxy to get the distance, and the new measurement puts NGC 1052-DF2 about 72 million light years from us, even more distant than before!

That makes things worse. It means the total brightness of the visible matter in the galaxy is higher (since it’s farther away than we thought) and so the dark matter content is even lower.

If we accept that the galaxy is truly at this distance it’s really hard to understand why it has no dark matter. There are some hypotheses on how a dark-matter-haloless dwarf galaxy can form, but they take some special conditions. One of them is that it forms near a much bigger galaxy that can strip the halo away from it. As it happens NGC 1052 is pretty close to DF2, so it’s possible this is what happened.

In the end these new Hubble images deepen the problem. It’s possible that the globular cluster velocities measured to get the galaxy’s total mass were off enough that the dark matter mass calculated is wrong, but that’s not covered by these new images. Perhaps more observations from ground-based telescopes can tighten that up.

Consider this whole thing an update, a chapter in the mystery novel that gives more information but doesn’t seem to help further the narrative other than dismissing a red herring. Fun, but there are still a lot of chapters to go.

## The supermassive black hole in our galaxy recently erupted… and we don't know why

In the exact center of our Milky Way galaxy sits a black hole. And not just any black hole, but a big one, what we call a supermassive black hole. At over 4 million times the Sun's mass, yeah, the name is apt.

It's usually pretty quiet, but in May 2019 it erupted, blasting out a pretty decently terrifying flare (Note: We're in absolutely no danger, since it's 26,000 light years away!) as astronomers watched.

The question is, why? Well, you know me by now: Let me give you a wee bit of background first.

We think every big galaxy has an SMBH (as those in the know call supermassive black holes), ranging from a few million to many billions of times the Sun's mass. These beasts form along with the galaxy, and both can affect each other's growth and behavior.

In some galaxies, gas and dust fall into the center, feeding the black hole. The material forms a huge disk, sometimes hundreds of light years across. Close to the center, friction heats the disk up to incredible temperatures, so it glows fiercely, becoming so luminous that it can outshine the hundreds of billions of stars in the galaxy itself!

Those are called active galaxies, and happily the Milky Way galaxy is not among them. We call ours quiescent, meaning it's not blasting our radiation. But that doesn't mean it's actually quiet…

Astronomers routinely monitor our supermassive black hole, which is called Sgr A* (literally pronounced "Sagittarius A star" (the "star" part is for historical reasons), or sometimes "Saj A star" for short). We have observations of it going back decades.

In May 2019, a team of astronomers was using the Keck 10-meter telescope to monitor Sgr A* in near infrared, just outside what our eyes can see (at wavelengths of 1.64 and 2.12 microns, where the reddest light our eyes can see is about 0.75 microns). What they saw in their data was astonishing: A very large flare was erupting from the black hole. They caught it as it was already fading, unfortunately, but it was still bright, as this animation shows:

Whoa! You can see the flare already in progress, fading over just a few hours. This was the brightest flare ever seen at these wavelengths, in fact. It dropped in brightness by a factor of 75 in just a couple of hours, and at one point dropped by a factor of 9 in just two minutes.

I did a little bit of math, and I find that very roughly, at its brightest, this flare was well over 2,000 times more luminous than the Sun at this wavelength — and mind you, they caught it after it peaked, so it's not clear how bright it actually got.

Images taken of the Milky Way’s supermassive black hole using the Keck telescope in May 2019 show it fading after a bright infrared flare (top row). The brightness plot (bottom row red circles indicate the times the images in the top row were taken) show it faded by nearly 5 magnitudes, about a factor of 75 in brightness. Credit: Do et al.

Sgr A* is known to fluctuate quite a bit, so the astronomers looked at these observations statistically to compare them with previous observations, and found that the odds of this flare happening just as a random fluctuation are extremely low, like 1 in 2,000. So it appears that something unusual happened at the black hole, something different, to cause it to flare this brightly.

Well, there are a couple of suspects.

Sgr A* isn't alone there in the center of our galaxy. For one thing, there are quite a few stars orbiting our Milky Way's monster. Most take decades to orbit it once, but one, called S2, gets closer than any other known star (it's the star immediately above Sgr A* in the video). Every 16 years, its elliptical orbit drops it a mere 20 billion kilometers from the SMBH. In human terms that's a long way — about four times the distance of Neptune from the Sun — but the gravity of Sgr A* is so ridiculously strong that it accelerates that star to a whopping 7,650 kilometers per second at its closest. That's 2% the speed of light!

The last pass was just last year, in May 2018. Astronomers observed it intently for a number of reasons, one of which was to check on some weird predictions of Einstein's Theory of Relativity (which, naturally, came through with flying colors). While that was all very cool, it's possible that this recent flare is tied to S2 somehow. It's a massive star, and such stars blow a wind of subatomic particles, just like the solar wind but much denser. If the wind is dense enough, and fell into the black hole, perhaps this is the cause of the flare…? However, the astronomers looked into that and determined it's unlikely S2's wind is strong enough to create such a big flare.

It's also possible that the close pass of the star gravitationally perturbed some of the gas around Sgr A*, causing an unusually large amount to fall in. That's harder to determine perhaps in 15 years, after the next pass, we'll be able to see if this happens again.

The other suspicious character is an object called G2, and to be honest no one knows exactly what it is. It was thought at first to be a dust cloud, because it gives off a similar signature of light in the infrared. It moves around Sgr A* on a 260 year orbit, and in 2014 it skimmed pretty close to the black hole, passing it by only about 30 billion km. That's close enough that a small dust cloud should have been torn apart by the tides from the SMBH… but it appeared to survive the encounter! So it may be a cloud with a small star in the middle, which holds it together. Another idea is that it started out life as a tight binary star, and sometime in the past repeated encounters with Sgr A* caused the two stars to merge. This would also blow off a lot of dust.

Either way, if G2 is shedding material, it too might orbit the black hole on a similar path. If a bigger blob of this stuff fell down onto Sgr A* (maybe due to S2?) then that would be a candidate for the source of the flare.

There are other possibilities, like an asteroid or comet stripped from a star system falling into the black hole the gravity would tear it apart, flinging some material away while gobbling down the rest. This too could cause a bright flare.

I'll note that flares in other wavelengths have been seen in the past in X-rays there are incredible flares, some creating jumps of a factor of 100,000 in the luminosity of X-rays coming from Sgr A*! These typically happen a few times per century and last for a few years. Just a few days ago the Neil Gehrels Swift satellite detected a large flare in X-rays from Sgr A*, where it blasting out over 30 times the Sun's total output of energy across the electromagnetic spectrum. Several other smaller flares have been detected by Swift recently as well. These may be related to the May infrared event. Or they may not be. We just don't know.

So it's not clear why this happened, or when it will happen again. So, the only thing to do is keep an eye on the black hole, so to speak, and keep watching it. Unfortunately, we're rapidly approaching the time of year when the Sun passes through Sagittarius, making observations like this impossible. We'll just have to wait a few months before starting up again. Hopefully, if Sgr A* decides to throw a tantrum again, it'll wait for us to be able to see it.

## Astronomers See Evidence of Supermassive Black Holes Forming Directly in the Early Universe

Super-Massive Black Holes (SMBH) are hard to explain. These gargantuan singularities are thought to be at the center of every large galaxy (our Milky Way has one) but their presence there sometimes defies easy explanation. As far as we know, black holes form when giant stars collapse. But that explanation doesn’t fit all the evidence.

The stellar-collapse theory does a good job of explaining most black holes. In that theory, a star at least five times more massive than our Sun begins to run out of fuel near the end of its life. Since the outward pressure of a star’s nuclear fusion is what supports it against the inward gravity from its own mass, something has to give when the fuel runs out.

The star undergoes a hypernova explosion, then collapses in on itself. What’s left is a black hole. Astrophysicists think that SMBHs start out this way, and grow into their enormous sizes by essentially ‘feeding’ on other matter. They swell in size, and sit in the center of their gravity kind of like a spider fattening up in the middle of its web.

The problem with that explanation is that it takes a long time to happen.

This artist’s impression shows the surroundings of a supermassive black hole, typical of that found at the heart of many galaxies. The black hole itself is surrounded by a brilliant accretion disc of very hot, infalling material and, further out, a dusty torus. There are also often high-speed jets of material ejected at the black hole’s poles that can extend huge distances into space. Image Credit: By ESO/L. Calçada – ESO website, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=39626793

Out there in the Universe, scientists have observed SMBHs that are ancient. In March of this year a group of astronomers announced the discovery of 83 SMBHs that are so ancient they defied our understanding. In 2017 astronomers discovered an 800 million solar mass black hole that was fully formed only 690 million years after the Big Bang. They came into existence in the earlier days of the Universe, before there was time to grow into their super-massive forms.

Many of these SMBHs are billions of times more massive than the Sun. They’re at such high red-shifts, that they must have been formed in the first 800 millions years after the Big Bang. But that’s not enough time for the stellar-collapse model to explain them. The question facing astrophysicists is, how did those black holes get so big in so little time?

A pair of researchers at Western University in Ontario, Canada, think they’ve figured it out. They have a new theory called ‘direct collapse’ that explains these incredibly ancient SMBHs.

Their paper is titled “The Mass Function of Supermassive Black Holes in the Direct-collapse Scenario” and is published in The Astrophysical Journal Letters. The authors are Shantanu Basu and Arpan Das. Basu is a recognized expert in the early stages of star formation and protoplanetary disk evolution. He’s also an astronomy professor at Western University. Das is also from Western’s Department of Physics and Astronomy.

The SMBH in this Subaru Telescope image is 13.05 billion light years from Earth. These ancient SMBHs have challenged our understanding of how black holes form. Image Credit: National Astronomical Observatory of Japan (NAOJ).

Their direct collapse theory says that the ancient super-massive black holes formed extremely quickly in very short time periods. Then suddenly, they stopped growing. They developed a new mathematical model to explain these rapidly-forming, ancient black holes. They say the the Eddington Limit, which is a balance between a star’s outward radiative force and the inward gravitational force, plays a role.

In these direct-collapse black holes, the Eddington Limit regulates the mass growth, and the researchers say that these ancient black holes can even exceed that limit by a small amount, in what they call super-Eddington accretion. Then, due to radiation produced by other stars and black holes, their production halted.

“Supermassive black holes only had a short time period where they were able to grow fast and then at some point, because of all the radiation in the universe created by other black holes and stars, their production came to a halt,” explains Basu in a press release. “That’s the direct-collapse scenario.”

“This is indirect observational evidence that black holes originate from direct-collapses and not from stellar remnants,” said Basu.

This new theory provides an effective explanation for what has been a thorny issue in astronomy for some time. Basu believes that these new results can be used with future observations to infer the formation history of the extremely massive black holes that exist at very early times in our universe.

## Exploring The Universe That Wasn’t

An illustration of multiple, independent Universes, causally disconnected from one another in an . [+] ever-expanding cosmic ocean, is one depiction of the Multiverse idea. Other Universes with different properties than our own may or may not exist, but if certain properties were even slightly different, our existence would not be admissable.

13.8 billion years ago, what we know today as our Universe began with the hot Big Bang. Filled with matter, antimatter and radiation in an almost uniform fashion, it expanded and gravitated in nearly perfect balance. As the Universe cooled, the matter and antimatter annihilated away, leaving a tiny, minuscule, but significant amount of matter behind. After 9.2 billion years, what would become our Solar System gradually began to form from a collapsing cloud of molecular gas, and after another 4.55 billion years or so, humanity first arose on planet Earth.

When we look out at the Universe from our perspective here and now, we only get a snapshot of existence, defined by the properties of the light, particles, and gravitational waves that we observe at the moment of their arrival. Based on all that we’ve seen, combined with our theories, frameworks, and models that reflect the fusion of those observations with the underlying laws of physics, we’ve come to understand the cosmos around us. But if things had been only a tiny bit different, our Universe would have been dramatically different. Here are five things that could have happened to change the course of our shared cosmic history.

Our Universe, from the hot Big Bang until the present day, underwent a huge amount of growth and . [+] evolution, and continues to do so. Our entire observable Universe was approximately the size of a soccer ball some 13.8 billion years ago, but has expanded to be

46 billion light-years in radius today. The complex structure that has arisen must have grown from seed imperfections early on.

1.) What if the Universe were actually perfectly uniform when it was born? This one is not something that’s greatly appreciated: the Universe, as we know it, couldn’t have been born perfectly smooth. If we had possessed an exactly equal amount of matter-and-antimatter-and-radiation everywhere, at all locations in space, going all the way back to the earliest moments of the hot Big Bang, every point in the Universe would experience an equal gravitational force pulling on it in all directions. In other words, the idea of gravitational growth and collapse relies on an initial imperfection to grow from. Without the seed, you can’t get the desired end result, like a star, galaxy, or something even larger.

The only hope we’d have would originate from the quantum nature of the Universe. Because we have quantum processes that cannot be avoided:

• inherent uncertainties in the positions and momenta of particles,
• inherent uncertainties between the energy in a system and the amount of time that passes,
• and exclusion rules that prevent certain particles from occupying identical quantum states,

### Mars, Venus And A ‘Super Solstice Strawberry Moon’ Sparkle In Twilight: What You Can See In The Night Sky This Week

some amount of imperfections will automatically arise even if there were none initially.

As our satellites have improved in their capabilities, they've probes smaller scales, more frequency . [+] bands, and smaller temperature differences in the cosmic microwave background. The temperature imperfections provide the seeds of structure formation without them, the only imperfections would arise from quantum effects, and would be

NASA/ESA AND THE COBE, WMAP AND PLANCK TEAMS PLANCK 2018 RESULTS. VI. COSMOLOGICAL PARAMETERS PLANCK COLLABORATION (2018)

From these quantum processes, you’d expect the initial imperfections to arise at around the 1-part-in-10 35 level, which is extremely tiny. For comparison, as informed by observations, our Universe was born with imperfections that arise at the 1-part-in-30,000 level. Although this, too, is small, it’s absolutely enormous compared to the tiny quantum fluctuations that exist today: more than 30 orders of magnitude larger.

Based on the way that imperfections grow in the Universe, it took somewhere around

100 million years for the largest of the initial fluctuations that the Universe started off with to form the first stars. If the Universe were born with fluctuations that were 1-part-in-10,000,000 instead, we’d very likely only be forming the first stars now gravitational growth takes a very long time unless you start from a substantially large seed. If our Universe were born exactly, perfectly uniform, there would be no structure, no stars, and no interesting chemical reactions to speak of anywhere in the cosmos.

There is a large suite of scientific evidence that supports the expanding Universe and the Big Bang. . [+] At every moment throughout our cosmic history for the first

6 billion years, the expansion rate and the total energy density balanced precisely, enabling our Universe to persist and form complex structures. This balance was essential.

2.) What if the expansion rate and the effects of gravitation were less perfectly balanced? This one is a bit tricky. We normally think of the Universe as a fairly stable place, but that’s only because there are two things that have been so well-balanced for so long: the rate at which the Universe expands and the decelerating effects of all the matter and radiation in the Universe. Today, these two effects don’t match, and that’s why we say the expansion of the Universe is accelerating.

6 billion years of the Universe’s history, they didn’t just match, they matched so perfectly well that what we know of as dark energy would have been completely undetectable, even if a potential alien civilization developed the exact tools we use today to measure the Universe. The farther back in time you go, the less important dark energy becomes relative to matter and radiation. And we can go back not just billions of years, but all the way back to the first tiny fraction-of-a-second after the hot Big Bang.

If the Universe had just a slightly higher matter density (red), it would be closed and have . [+] recollapsed already if it had just a slightly lower density (and negative curvature), it would have expanded much faster and become much larger. The Big Bang, on its own, offers no explanation as to why the initial expansion rate at the moment of the Universe's birth balances the total energy density so perfectly, leaving no room for spatial curvature at all and a perfectly flat Universe. Our Universe appears perfectly spatially flat, with the initial total energy density and the initial expansion rate balancing one another to at least some 20+ significant digits.

Ned Wright's cosmology tutorial

Here, we can find all the matter and energy we have in the Universe today compressed into a much, much smaller region of space. At this time, the Universe was not only hotter and denser, but expanded much, much more quickly than it’s expanding today. In fact, one way to picture the expanding Universe is to treat it as a race: between the initial expansion rate — whatever that rate what when the hot Big Bang first occurred — and the total effects of all the matter, antimatter, neutrinos, radiation, etc., that are present.

What’s remarkable is when we consider how perfectly balanced these two quantities must have been. Today, the Universe has a density of about 1 proton per cubic meter of space. But early on, it had a density that was more like quintillions of kilograms per cubic centimeter of space. If you would have increased or decreased that density by just 0.00000000001%, the Universe would have:

• recollapsed on itself, ending in a Big Crunch after less than 1 second, in the case of an increase,
• or expanded so quickly that no protons and electrons would ever have found one another to form even a single atom in the Universe, in the case of a decrease.

This incredible balance, along with the need for it, highlights just how precarious our existence in this Universe is.

Quarks and electrons come in slightly greater numbers than antiquarks and positrons. In a completely . [+] symmetric Universe, matter and antimatter annihilate away leaving trace and equal amounts of both. But in our Universe, matter dominates, indicating an early, fundamental asymmetry.

E. Siegel / Beyond The Galaxy

3.) What if there had been exactly equal amounts of matter and antimatter? This is another problematic one for us, and in fact it’s one of the greatest unsolved problem in all of physics: why do we live in a Universe with more matter than antimatter? This puzzle has many possible resolutions, but no definitive answer. What we can say, for certain, is that:

• in the early stages of the hot Big Bang, the Universe should have been perfectly symmetric between matter and antimatter,
• and that somehow, some process occurred that resulted in the existence of approximately 1,000,000,001 matter particles for every 1,000,000,000 antimatter particles,
• and when the excess annihilated away, we were left with that tiny bit of matter amidst a leftover bath of radiation.

That radiation still survives, as does the matter, which is why we can reconstruct what happened at early times.

How the Universe would have evolved if there weren't a matter-antimatter asymmetry. Instead of . [+] particles and antiparticles annihilating so that only a small number of particles were left, a symmetric Universe would annihilate everything away billions of times more efficiently, until only a sparse number of particles and antiparticles remained.

We still don’t know how it happened, but we do know what our Universe would have looked like if we didn’t generate a matter-antimatter asymmetry: the matter and antimatter would have annihilated away, not completely, but until there was so little matter and antimatter left that the individual particles that were left — protons and antiprotons, electrons and positrons, etc. — would simply no longer find each other.

Today’s Universe, you’ll recall, has about

1 proton per cubic meter of space: if you smeared out the entire Universe and drew a box that was 1 meter × 1 meter × 1 meter, you’d expect to find about 1 proton inside. When you work out the math for what happens if matter and antimatter annihilated away from a perfectly symmetric state, you’d find a very different Universe. Radiation would keep scattering off of these particles for tens of millions of years, rather than just a few hundred thousand, and the average density of all forms of matter and antimatter would be the equivalent only

1 proton (or antiproton) per cubic mile: a box that was 1 mile × 1 mile × 1 mile, or about 10 billion times less dense than the Universe we have today.

If our Universe hadn’t created a matter-antimatter asymmetry early on, none of the remarkable steps that came afterwards to lead to our existence could have taken place.

In three different wavelength bands, the structure of the stars in galaxy NGC 1052-DF4 can be seen . [+] being elongated along the line-of-sight towards nearby large galaxy NGC 1035. This galaxy, which lacks dark matter, is actively being torn apart without this "glue" to hold itself together.

M. Montes et al., ApJ, 2020, accepted

4.) What if there hadn’t been any dark matter? This one is a fascinating consideration that’s generally greatly underappreciated. Most of us think about dark matter as the “glue” that holds the largest structures in the Universe together: things like the cosmic web and enormous galaxy clusters. But dark matter also does two enormously important things we don’t typically think about:

• it provides the majority of the gravitational mass that both forms all galaxies in the Universe and continues to hold them together,
• and it prevents structure from being “washed out” by the interactions that exist between normal matter and radiation.

Take dark matter away, and what happens? The small-scale structure you’d attempt to form wouldn’t exist, as the early radiation-dominated phase of the Universe would wash those imperfections away. Meanwhile, the galaxies that you did form would undergo one burst of star formation, and then those stars would boil all the surrounding matter away, ejecting it from the galaxy entirely. In a Universe with no dark matter, only that first generation of stars would exist, meaning there would be no rocky planets, no biochemistry, and no life.

The blue "shading" represent the possible uncertainties in how the dark energy density was/will be . [+] different in the past and future. The data points to a true cosmological "constant," but other possibilities are still allowed. As matter becomes less and less important, dark energy becomes the only term that matters. The expansion rate has dropped over time, but will now asymptote to around 55 km/s/Mpc.

5.) What if dark energy weren’t constant in space or time? This is the one possibility that’s still on the table for our Universe: that dark energy might evolve in some fashion. To the best of our observational limits, it certainly looks and behaves like a cosmological constant — as a form of energy inherent to the fabric of space itself — where the energy density remains constant in time and all throughout space.

But we don’t have constraints on how dark energy behaved (or whether it even existed!) for roughly the first

50% of our Universe’s history, and we only observe it to be a constant to the limits of our current precision. Three telescopes will improve on this in the near future: the ESA’s EUCLID, the NSF’s Vera Rubin Observatory, and NASA’s Nancy Roman telescope, the last of which should measure whether dark energy changes at all to a precision of just

If dark energy strengthens, the Universe could rip apart. If dark energy weakens or reverses sign, the Universe could yet recollapse. And if dark energy decays, the Universe as we know it could end. None of these things have happened yet, but if the Universe were only slightly different, any one of them could have taken place in the past, precluding our existence from occurring at all.

How likely or unlikely was our Universe to produce a world like Earth? And how plausible would those . [+] odds be if the fundamental constants or laws governing our Universe were different? Most Universes that we can imagine would not give rise to potential observers, like human beings. A Fortunate Universe, from whose cover this image was taken, is one such book that explores these issues.

Geraint Lewis and Luke Barnes

All of this, when taken together, leads us to a fascinating conclusion: if any of these things were — in any way — substantially different from the way they are, it would have been a physical impossibility for human beings to have arisen as we did within the Universe. A Universe that was too smooth would have failed to create stars and galaxies in time a Universe that expanded too quickly or slowly wouldn’t have remained stable for long enough to form anything interesting. A Universe without more matter than antimatter couldn’t have formed stars, and a Universe without dark matter couldn’t have hung onto their remnants to form planets.

In many ways, we’re extremely fortunate to have gotten the Universe that we occupy, as if any one of a great number of things were even a little bit different, the Universe would not have admitted the existence of humans, or any intelligent observer, as a possibility. But in this cosmos of ours, exactly the way it is, we can observe some 2 trillion galaxies. Around one of the

400 billion stars in one of them, the Milky Way, life took hold, survived, thrived, and evolved. After more than 4 billion years, human beings arose, and now we look out at the Universe to learn our place in it. It may not have been an inevitable journey from the Big Bang to us, but it sure has been a remarkable one.

## “As Big as a Galaxy?” –The Search for Largest Black Hole in the Universe

Is it possible that an as yet undetected galaxy-sized black hole exists somewhere in the distant universe? The reality may actually prove to be something even more bizarre. On July 26, The Daily Galaxy reported on the discovery forty years ago of a supermassive black hole powering microquasar SS 433, some 5,000 times the size of our Solar System located about 18 000 light-years away in the constellation of Aquila (The Eagle).

This past April, the Event Horizon Telescope (EHT) team unveiled humanity’s first image of a supermassive black hole –described as the Gates of Hell and the End of Spacetime– the picture of galaxy Messier 87’s central supermassive black hole. A monster the size of our solar system, and bigger, with the mass of six and a half billion suns, with a ring of gas—in hues of red, orange, and yellow—glowing around it, the shadow cast by the event horizon, predicted by Einstein’s theory of general relativity.

The April event was as epic as the Apollo 11 landing on the Moon, with the world viewing its first image of what had once been purely theoretical, a black hole at the heart of galaxy M87, the size of our solar system, and bigger, with the mass of six and a half billion suns that was captured by a lens the size of planet Earth and 4,000 times more powerful than the Hubble Space Telescope. M87’s black hole is frozen in time it was 55 million years ago, because it’s so far away the light took that long to reach us.

“Over those eons, we emerged on Earth along with our myths, differentiated cultures, ideologies, languages and varied beliefs,” says astrophysicist Janna Levin with Columbia University.

Astronomers have theorized that the galaxy that harbors the black hole grew to its massive size by merging with several other black holes in elliptical galaxy M87, the largest, most massive galaxy in the nearby universe thought to have been formed by the merging of 100 or so smaller galaxies. The M87 black hole’s large size and relative proximity, led astronomers to think that it could be the first black hole that they could actually “see.”

Paradoxically, the smallest objects in the known universe

Black holes, paradoxically, the smallest objects in the known universe, have outsize effects on entire galaxies. Black holes are where the quantum world and the gravitational world come together, says Shepard Doeleman, Event Horizon Telescope director and astronomer with the Harvard Smithsonian Center for Astrophysics. They are “the central mystery of our age, a one-way door out of our universe.”

“What’s inside is a singularity, where all the forces become unified because gravity finally is strong enough to compete with all the other forces—the strong, weak, and electromagnetic. But we can’t see the singularity. “The universe has cloaked it in the ultimate invisibility cloak. We don’t know what happens in there.”

Or, as described by Ellie Mae O’Hagan with The Guardian,“the point at which every physical law of the known universe collapses. Perhaps it is the closest thing there is to hell: it is an abyss, a moment of oblivion.”

On June 7, 2019 The Daily Galaxy reported on the discovery of a black hole that is growing so rapidly that it’s as luminous as 700 trillion suns, shining thousands of times more brightly than an entire galaxy due to all of the gases it sucks in daily that cause lots of friction and heat.

How this drainpipe into eternity grew to such mass so early after the Big Bang is a profound puzzle for physics. “If this monster was at the center of the Milky Way it would likely make life on Earth impossible with the huge amounts of x-rays emanating from it,” said Christian Wolf, with the Australian National University Research School of Astronomy and Astrophysics who made the momentous detection.

”It would appear 10 times brighter than a full moon, an incredibly bright pin-point star that would almost wash out all of the stars in the sky. It’s probably 10,000 times brighter than the galaxy it lives in.” So bright, that it is blinding our view and we can’t see the galaxy itself.

Devours a mass equivalent to our sun every two days

This newly observed object is known officially as SMSS J215728.21-360215.1 In May of 2018 , astronomers at ANU found this fastest-growing black hole known in the universe, describing it as a monster that devours a mass equivalent to our sun every two days. The astronomers have looked back more than 12 billion years to the early dark ages of the Universe, when this supermassive black hole was estimated to be the size of about 20 billion suns with a one per cent growth rate every one million years.

More recently, astronomers have observed a super massive black hole, 700 million light years away, in the center of a super-giant elliptical galaxy This black hole is growing so rapidly that it’s as luminous as 700 trillion suns, shining thousands of times more brightly than an entire galaxy due to all of the gases it sucks in daily that cause lots of friction and heat. How this drainpipe into eternity grew to such mass so early after the Big Bang is a profound puzzle for physics.

Would likely make life on Earth impossible

“If this monster was at the center of the Milky Way it would likely make life on Earth impossible with the huge amounts of x-rays emanating from it,” said Wolf. ”It would appear 10 times brighter than a full moon, an incredibly bright pin-point star that would almost wash out all of the stars in the sky. It’s probably 10,000 times brighter than the galaxy it lives in.” So bright, that it is blinding our view and we can’t see the galaxy itself.

More recently, astronomers have detected a super massive black hole (SMBH) that’s 40 billion times more massive than our Sun that if situated in the center of our Solar System it would extend out to Pluto and beyond. The SMBH lies center of a super-giant elliptical galaxy called Holmberg 15A, about 700 million light years away, in the center of the Abell 85 galaxy cluster.

But Holmberg 15A pales in comparison to the Ultra Massive Black Hole (UMBH) at the center of TON 618, an extremely luminous quasar over 10 billion light years away. This monster is 66 billion times more massive than the Sun. But that UMBH was measured indirectly, so its mass measurement might be revised.

Embedded within a vast sphere of black holes

Does a supermassive black hole exist that’s as big as a galaxy? The reality might be something even more bizarre.

Astrophysicists say there’s most likely a limit of about 50 billion solar masses before its disc of gas collapses and it stops growing. But if two black holes merge that have already reached that limit, then a UMBH that’s up to 100 billion solar masses may be possible, not quite a galaxy, but still incomprehensible by mere mortal homo sapiens.

In a 2016 post, The Daily Galaxy reported that according to Alexander Kashlinsky, an astrophysicist at NASA Goddard Space Flight Center, black holes formed in the universe’s first fraction of a second — “could work as dark matter,”

“If this is correct,” said Kashlinsky, “then all galaxies, including our own, are embedded within a vast sphere of black holes each about 30 times the sun’s mass.”

“Future LIGO observing runs will tell us much more about the universe’s population of black holes, and it won’t be long before we’ll know if the scenario I outline is either supported or ruled out,” Kashlinsky said. He leads the science team centered at Goddard that is participating in the European Space Agency’s Euclid mission, which is currently scheduled to launch in 2020.

## There’s a Black Hole With 34 Billion Times the Mass of the Sun, Eating Roughly a Star Every Day

In the 1960s, astronomers began theorizing that there might be black holes in the Universe that are so massive – supermassive black holes (SMBHs) – they could power the nuclei of active galaxies (aka. quasars). A decade later, astronomers discovered that an SMBH existed at the center of the Milky Way (Sagitarrius A*) and by the 1990s, it became clear that most large galaxies in the Universe are likely to have one.

Since that time, astronomers have been hunting for the largest SMBH they can find, in the hopes that can see just how massive these things get! And thanks to new research led by astronomers from the Australian National University, the latest undisputed heavy-weight contender has been found! With roughly 34 billion times the mass of our Sun, this SMBH (J2157) is the fastest-growing black hole and largest quasar observed to date.

The team’s study, which recently appeared in The Monthly Notices of the Royal Astronomical Society, was led by Dr. Christopher A. Onken – the operations manager of the SkyMapper telescope. He was joined by researchers from the Research School of Astronomy and Astrophysics (RSAA) and the Center for Gravitational Astrophysics (CGA) at ANU, as well as the European Southern Observatory (ESO) and Steward Observatory.

NASA’s Spitzer Space Telescope captured this stunning infrared image of the center of the Milky Way Galaxy, where the black hole Sagitarrius A resides. Credit: NASA/JPL-Caltech

The same team was responsible for discovering J2157, which they did back in 2018, using data from the Gaia observatory, the Wide-field Infrared Survey Explorer (WISE) space telescope, and the SkyMapper Southern Sky Survey. That particular study was led by Christian Wolf, a member of the Australian Research Council’s Centre of Excellence in All-sky Astrophysics (CAASTRO), who also participated in this latest study.

As they indicated at the time, J2157 is the brightest quasar observed in the known Universe to date, which they attributed to the presence of an SMBH at its center. What’s more, they were able to rule out the possibility that its luminosity was the result of gravitational lensing, where the presence of intervening galaxies and other massive objects were responsible for magnifying J2157’s brightness.

This was a strong possibility, given that light J2157 is visible 12.5 billion light-years from Earth, and therefor has to traverse a huge distance in space and time to reach us. For this latest study, Dr. Onken and the team relied on data from the ESO’s Very Large Telescope (VLT) in Chile to constrain the distance and mass of this SMBH at the core of J2157. As Dr. Onken said in a recent ANU press release, what they found was rather surprising:

“The black hole’s mass is also about 8,000 times bigger than the black hole in the center of the Milky Way. If the Milky Way’s black hole wanted to grow that fat, it would have to swallow two-thirds of all the stars in our Galaxy. We’re seeing it at a time when the universe was only 1.2 billion years old, less than 10 percent of its current age. It’s the biggest black hole that’s been weighed in this early period of the Universe.”

Already, the team had inklings that J2157 contained a rapidly-growing SMBH that consumed stars in the central region of its galaxy on a regular basis. But the fact that it was the fastest-growing SMBH in the Universe just 1.2 billion years after the Big Bang was nothing short of astounding. As Dr Fuyan Bian, a staff astronomer at the European Southern Observatory (ESO), said:

“We knew we were onto a very massive black hole when we realized its fast growth rate. How much black holes can swallow depends on how much mass they already have. So, for this one to be devouring matter at such a high rate, we thought it could become a new record holder. And now we know.”

But equally significant is what J2157 can teach us about the early Universe and its subsequent evolution. For some time, astronomers have been looking for more examples of SMBHs in the early Universe to see how they affected the evolution of galaxies and the cosmos as a whole. At the same time, they have been looking for answers as to how SMBHs could have grown so large in such a short space of time.

While these questions remain unresolved, the discovery of this ancient and most-massive of supermassive black holes could provide some very helpful clues. Already, the team behind this discovery is searching for more black holes that existed at the center of galaxies shortly after the Big Bang, in the hopes that they might find some additional clues.

Image taken by the Hubble Space Telescope of a 5000-light-year-long jet ejected from the active galaxy M87. Credit: NASA/The Hubble Heritage Team (STScI/AURA)

Said team member Dr. Fuyan Bian, a staff astronomer at the European Southern Observatory (ESO):

“With such an enormous black hole, we’re also excited to see what we can learn about the galaxy in which it’s growing. Is this galaxy one of the behemoths of the early Universe, or did the black hole just swallow up an extraordinary amount of its surroundings? We’ll have to keep digging to figure that out.”

One of the most important developments in the fields of astronomy and astrophysics in the past few decades has been the ability to see farther and with greater clarity. By looking deeper into the cosmos, they have also been able to look farther back in time and see what the Universe looked like at a very young age. This has allowed scientists to test cosmological theories about how the Universe has grown and evolved ever since.

With all the new developments that expected in the ensuing years and decades – which include the deployment of next-generation telescopes, AI and machine learning, and increased data-sharing – scientists anticipate that the most enduring cosmological questions will soon be answered!

## Scientists Unravel Secrets of Monster Black Hole at Center of Milky Way

Supermassive black hole last erupted two million years ago, and will again.

For years astronomers have been puzzled as to why our Milky Way galaxy's "volcano"—a supermassive black hole (SMBH) at its core—is dormant today.

It seems the answer may simply be that we didn't catch the cosmic monster—weighing at least four million times the mass of our sun—feeding at the right time, according to a new study.

"If we had been around to see it two million years ago, the situation would have been very different," said study co-author Philip Maloney of the University of Colorado in Boulder.

"The Milky Way's black hole was maybe ten million times brighter [then]," he said. "I don't think anyone really had any expectation that SMBH might vary in luminosity by such a huge factor on such a short—relatively speaking—time scale."

Astronomers have long suspected there was an ancient outburst from the hibernating black hole, but it's only now that they believe they have found an actual "fossil imprint" of the cosmic monster's last big meal.

The international team's new theory points to a lacy filament of gas, mostly hydrogen, called the Magellanic Stream, which can be seen trailing behind our galaxy's two small companion galaxies: the Large and Small Magellanic Clouds.

Maloney believes powerful beams of energy erupting from the SMBH two million years ago hit the stream—causing its hydrogen gas to get ionized and light up, much like the glow of auroras we see here on Earth. This ionization of the Magellanic Stream has puzzled scientists since its discovery two decades ago.

"No one has been able previously to come up with a good model to explain the ionization," said Maloney.

The team now suspects that this glowing stream of extragalactic gas may be the fossil imprint of the SMBH eruption two million years ago. (See black hole photos.)

The estimated orientation and amount of energy of the original outburst, including the cooling time of the illuminated stream, fit very well with the proposed model.

Further evidence for a giant eruption sometime in the distant past has also come in the form of recently detected gamma ray and radio wave signatures of two giant, hot bubbles of gas called Fermi bubbles. Thought to have been belched out by the SMBH, the Fermi bubbles sit above and below the plane of the Milky Way.

The question is not if there will be another eruption, but when, scientists say.

Infrared and x-ray satellites have been able to peer into the heart of our galaxy and detect radiation flowing out from the region around the black hole as it rips apart the small, orbiting clouds of gas falling toward it and colliding with it.

Astronomers now believe many gas clouds orbit the SMBH today, and they could trigger a future outburst—in fact, it may be just around the corner.

"They have been monitoring a cloud and predict that it will fall into the black hole at some point in the next year however, the amount of material will be far less than the event that illuminated the stream," said co-author Greg Madsen, an astronomer at the University of Cambridge.

"It will be much fainter and will pose no threat to Earth, but several powerful telescopes will be poised and ready to watch what happens."

This research has been accepted for publication in the Astrophysical Journal.

Astronomers are beginning to understand what happens when black holes get the urge to roam through the Milky Way. Typically, a supermassive black hole (SMBH) exists at the core of a massive galaxy. But sometimes SMBHs may “wander” throughout their host galaxy, remaining far from the center in regions such as the stellar halo, a nearly spherical area of stars and gas that surrounds the main section of the galaxy.

May Impact Our Solar System Every 100 Billion Years

“It is extremely unlikely that any wandering supermassive black hole will come close enough to our Sun to have any impact on our solar system,” said lead author Michael Tremmel , a postdoctoral fellow at the Yale Center for Astronomy and Astrophysics. “We estimate that a close approach of one of these wanderers that is able to affect our solar system should occur every 100 billion years or so, or nearly 10 times the age of the universe.”

“Over the last few years I’ve been excited about a growing number of detections of luminous sources that are set off from the centers of their galaxies,” wrote Tremmel in an email to The Daily Galaxy. “For example, in 2019 astronomers created a catalog of objects that are called hyperluminous x-ray sources, which are potential candidates for supermassive black holes. In 2020, discoveries showed radio sources consistent with supermassive black holes in dwarf galaxies.”

We’re Still Only Scratching the Surface

“Our ability to find low luminosity sources is getting better, as is our ability to detect the presence of multiple closeby sources, so-called Dual Active Galactic Nuclei,” Tremmel wrote in his email. “There is also progress in finding black holes through dynamical measurements (i.e. measuring the motions of nearby stars for their gravitational influence). These are SMBHs in the centers of what are thought to be the core remnants of a once much larger galaxy. It is important to note that all of these detections are in other galaxies and not the Milky Way specifically.”

“Put together,’ Tremmel wrote, “these observations speak to the fact that SMBHs far from the galactic centers are likely a common occurrence, though we are still only scratching the surface.”

Astronomers theorize that this phenomenon often occurs as a result of mergers between galaxies. A smaller galaxy will join with a larger, main galaxy, depositing its own, central SMBH onto a wide orbit within the new host.

Milky Way Should Host Several Supermassive Black Holes –All Invisible

In the 2018 study published in the Astrophysical Journal Letters, researchers from Yale, the University of Washington, Institut d’Astrophysique de Paris, and University College London predict that galaxies with a mass similar to the Milky Way should host several supermassive black holes. The team used a new, state-of-the-art cosmological simulation, Romulus, to predict the dynamics of SMBHs within galaxies with better accuracy than previous simulation programs.

Tremmel said that since wandering SMBHs are predicted to exist far from the centers of galaxies and outside of galactic disks, they are unlikely to accrete more gas—making them effectively invisible. “We are currently working to better quantify how we might be able to infer their presence indirectly,” Tremmel said.

The Daily Galaxy, Maxwell Moe , astrophysicist, NASA Einstein Fellow , University of Arizona via Yale University

The Galaxy Report newsletter brings you twice-weekly news of space and science that has the capacity to provide clues to the mystery of our existence and add a much needed cosmic perspective in our current Anthropocene Epoch.

Astronomers are beginning to understand what happens when black holes get the urge to roam through the Milky Way. Typically, a supermassive black hole (SMBH) exists at the core of a massive galaxy. But sometimes SMBHs may “wander” throughout their host galaxy, remaining far from the center in regions such as the stellar halo, a nearly spherical area of stars and gas that surrounds the main section of the galaxy.

Astronomers theorize that this phenomenon often occurs as a result of mergers between galaxies in an expanding universe. A smaller galaxy will join with a larger, main galaxy, depositing its own, central SMBH onto a wide orbit within the new host.

“It is extremely unlikely that any wandering supermassive black hole will come close enough to our Sun to have any impact on our solar system,” said lead author Michael Tremmel, a postdoctoral fellow at the Yale Center for Astronomy and Astrophysics. “We estimate that a close approach of one of these wanderers that is able to affect our solar system should occur every 100 billion years or so, or nearly 10 times the age of the universe.”

In the 2018 study published in the Astrophysical Journal Letters, researchers from Yale, the University of Washington, Institut d’Astrophysique de Paris, and University College London predict that galaxies with a mass similar to the Milky Way should host several supermassive black holes. The team used a new, state-of-the-art cosmological simulation, Romulus, to predict the dynamics of SMBHs within galaxies with better accuracy than previous simulation programs.

Tremmel said that since wandering SMBHs are predicted to exist far from the centers of galaxies and outside of galactic disks, they are unlikely to accrete more gas—making them effectively invisible. “We are currently working to better quantify how we might be able to infer their presence indirectly,” Tremmel said.

On March 9th, we reported that after conducting a cosmic inventory to calculate and categorize stellar-remnant black holes, astronomers from the University of California concluded that there are probably tens of millions of the enigmatic, dark objects in the Milky Way – far more than expected.

In stark contrast to the predictions of the Yale team, is physicist George Chapline’s conjecture that there has never been direct evidence of a central black hole,” while acknowledging there are objects that general relativity would predict are black holes at the centers of galaxies. “Ironically, Einstein also didn’t believe in black holes even though he created general relativity.”

Compared to the supermassive black holes in the centers of other galaxies, our black hole, Sagittarius A*, is strangely quiet. But Chapline thinks it’s more than quiet: he predicts that we’ll soon find that it does not exist.

Chapline, at the Lawrence Berkeley National Laboratory, expects to have his prediction that black holes don’t exist confirmed with the release of findings by the Event Horizon Telescope—really a virtual telescope with an effective diameter of the Earth—that has been pointing at the Milky Way’s central supermassive black hole for the last several years.

## “Oddball” Galaxy Contains the Biggest Black Hole Yet

It’s thought that at the heart of most if not every spiral galaxy (as well as some dwarf galaxies) there’s a supermassive black hole, by definition containing enormous amounts of mass — hundreds of millions, even billions of times the mass of our Sun packed into an area that would fit inside the orbits of the planets. Even our own galaxy has a central SMBH — called Sgr A*, it has the equivalent of 4.1 million solar masses.

Now, astronomers using the Hobby-Eberly Telescope at The University of Texas at Austin’s McDonald Observatory have identified what appears to be the most massive SMBH ever found, a 17 billion solar mass behemoth residing at the heart of galaxy NGC 1277.

Located 220 million light-years away in the constellation Perseus, NGC 1277 is a lenticular galaxy only a tenth the size of the Milky Way. But somehow it contains the most massive black hole ever discovered, comprising a staggering 14% of the galaxy’s entire mass.

“This is a really oddball galaxy,” said Karl Gebhardt of The University of Texas at Austin, a team member on the research. “It’s almost all black hole. This could be the first object in a new class of galaxy-black hole systems.”

The study was led by Remco van den Bosch, who is now at the Max Planck Institute for Astronomy (MPIA).

It’s estimated that the size of this SMBH’s event horizon is eleven times the diameter of Neptune’s orbit — an incredible radius of over 300 AU.

How the diamater of the black hole compares with the orbit of Neptune (D. Benningfield/K. Gebhardt/StarDate)

Although previously imaged by the Hubble Space Telescope, NGC 1277’s monster black hole wasn’t identified until the Hobby-Eberly Telescope Massive Galaxy Survey (MGS) set its sights on it during its mission to study the relationship between galaxies and their central black holes. Using the HET data along with Hubble imaging, the survey team calculated the mass of this black hole at 17 billion solar masses.

“The mass of this black hole is much higher than expected,” said Gebhardt, “it leads us to think that very massive galaxies have a different physical process in how their black holes grow.”

To date, the HET team has observed 700 of their 800 target galaxies.

In the video below, Remco van den Bosch describes the discovery of this unusually super supermassive black hole:

Read more on the UT Austin’s McDonald Observatory press release here, or this press release from the Max Planck Institute for Astronomy.