# How much damage would collision with a similar mass primordial black hole do to earth?

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All this talk of Planet 9 perhaps being a primordial black hole (PBH) made me wonder how dangerous a PBH collision with earth would really be.

Specifically, if earth collided with a PBH of 1 earth mass, traveling fast enough that they didn't end up orbiting each other, what would happen?

Edit: From a paper asking Can one detect passage of small black hole through the Earth? the analysis was that for an approximately proton-volume and mountain-mass sized PBH

"It creates a long tube of heavily radiative damaged material, which should stay recognizable for geological time."

but is otherwise pretty hard to detect.

What would change if the PBH were the mass of the earth and the volume of a large marble? How slow would it have to be going before it really messed things up?

Consider an initially stationary particle of matter and suppose a 1 Earth mass black hole flies past it at speed $$v$$ on a trajectory that passes the initial position of the particle at distance $$r$$. The particle will be mainly affected by the gravity during a time period of roughly $$r/v$$ (up to some "geometric" constants), during which time it will accelerate at roughly $$GM/r^2$$. This means that it will move a distance about $$GM/r^2 imes (r/v)^2 = GM/v^2$$. So if this is small compared to $$r$$ it will be left "more or less" where it was, rather than being ripped away. So we can expect a hole of diameter a few times $$GM/v^2$$. $$GM$$ is about $$4 imes 10^{14}$$ so to keep the hole diameter to say 1m you could need $$v$$ about $$2 imes 10^7 m/s$$ which is about $$0.07c$$.

We can also estimate the typical velocity change achieved by our test particle from this interaction, which is $$GM/r^2 imes r/v = GM/rv$$, giving a KE per unit mass of about $$G^2M^2/r^2v^2$$.

So, suppose the Earth has density $$ho$$ and radius $$R$$ the cylindrical shell of thickness $$dr$$ will mass $$R ho rdr$$ (still ignoring "small" constants like $$2pi$$). That shell will acquire kinetic energy $$G^2M^2R ho dr/rv^2$$ from the interaction. Integrating from $$GM/v^2$$ to $$R$$ we get a total energy deposited in the parts of the Earth which are not "ripped away". $$frac{G^2M^2R ho}{v^2}logfrac{Rv^2}{GM}$$

Using $$R = 6 imes 10^6$$, $$GM = 4 imes 10^{14}$$, $$ho = 5000$$, and $$v = 2 imes 10^7$$ (all SI units) we get about $$10^{25}J$$, not enough to actual destroy the Earth (Earth's gravitational binding energy is about $$10^{32}J$$) but about $$10^{10}$$ megatons or an earthquake of about 13 on the Richter scale.

A black hole moving 1000 times slower (typical solar system velocity) would essentially destroy the Earth.

## Micro black hole

Micro black holes, also called quantum mechanical black holes or mini black holes, are hypothetical tiny black holes, for which quantum mechanical effects play an important role. [1] The concept that black holes may exist that are smaller than stellar mass was introduced in 1971 by Stephen Hawking. [2]

It is possible that such quantum primordial black holes were created in the high-density environment of the early Universe (or Big Bang), or possibly through subsequent phase transitions. They might be observed by astrophysicists through the particles they are expected to emit by Hawking radiation. [ citation needed ]

Some hypotheses involving additional space dimensions predict that micro black holes could be formed at energies as low as the TeV range, which are available in particle accelerators such as the Large Hadron Collider. Popular concerns have then been raised over end-of-the-world scenarios (see Safety of particle collisions at the Large Hadron Collider). However, such quantum black holes would instantly evaporate, either totally or leaving only a very weakly interacting residue. [ citation needed ] Beside the theoretical arguments, the cosmic rays hitting the Earth do not produce any damage, although they reach energies in the range of hundreds of TeV.

## What happens when black holes collide?

The more massive the object, the more it distorts spacetime. Credit: LIGO/T. Pyle

The sign of a truly great scientific theory is by the outcomes it predicts when you run experiments or perform observations. And one of the greatest theories ever proposed was the concept of Relativity, described by Albert Einstein in the beginning of the 20th century.

In addition to helping us understand that light is the ultimate speed limit of the universe, Einstein described gravity itself as a warping of spacetime.

He did more than just provide a bunch of elaborate new explanations for the universe, he proposed a series of tests that could be done to find out if his theories were correct.

One test, for example, completely explained why Mercury's orbit didn't match the predictions made by Einstein. Other predictions could be tested with the scientific instruments of the day, like measuring time dilation with fast moving clocks.

Since gravity is actually a distortion of spacetime, Einstein predicted that massive objects moving through spacetime should generate ripples, like waves moving through the ocean.

Just by walking around, you leave a wake of gravitational waves that compress and expand space around you. However, these waves are incredibly tiny. Only the most energetic events in the entire universe can produce waves we can detect.

It took over 100 years to finally be proven true, the direct detection of gravitational waves. In February, 2016, physicists with the Laser Interferometer Gravitational Wave Observatory, or LIGO announced the collision of two massive black holes more than a billion light-years away.

Any size of black hole can collide. Plain old stellar mass black holes or supermassive black holes. Same process, just on a completely different scale.

Let's start with the stellar mass black holes. These, of course, form when a star with many times the mass of our sun dies in a supernova. Just like regular stars, these massive stars can be in binary systems.

Imagine a stellar nebula where a pair of binary stars form. But unlike the sun, each of these are monsters with many times the mass of the sun, putting out thousands of times as much energy. The two stars will orbit one another for just a few million years, and then one will detonate as a supernova. Now you'll have a massive star orbiting a black hole. And then the second star explodes, and now you have two black holes orbiting around each other.

As the black holes zip around one another, they radiate gravitational waves which causes their orbit to decay. This is kind of mind-bending, actually. The black holes convert their momentum into gravitational waves.

As their angular momentum decreases, they spiral inward until they actually collide. What should be one of the most energetic explosions in the known universe is completely dark and silent, because nothing can escape a black hole. No radiation, no light, no particles, no screams, nothing. And if you mash two black holes together, you just get a more massive black hole.

Colliding black holes. Credit: LIGO/A. Simonnet

The gravitational waves ripple out from this momentous collision like waves through the ocean, and it's detectable across more than a billion light-years.

This is exactly what happened earlier this year with the announcement from LIGO. This sensitive instrument detected the gravitational waves generated when two black holes with 30 solar masses collided about 1.3 billion light-years away.

This wasn't a one-time event either, they detected another collision with two other stellar mass black holes.

Regular stellar mass black holes aren't the only ones that can collide. Supermassive black holes can collide too.

From what we can tell, there's a supermassive black hole at the heart of pretty much every galaxy in the universe. The one in the Milky Way is more than 4.1 million times the mass of the sun, and the one at the heart of Andromeda is thought to be 110 to 230 million times the mass of the sun.

Arial view of LIGO Livingston. Credit: The LIGO Scientific Collaboration

In a few billion years, the Milky Way and Andromeda are going to collide, and begin the process of merging together. Unless the Milky Way's black hole gets kicked off into deep space, the two black holes are going to end up orbiting one another.

Just with the stellar mass black holes, they're going to radiate away angular momentum in the form of gravitational waves, and spiral closer and closer together. Some point, in the distant future, the two black holes will merge into an even more supermassive black hole.

The Milky Way and Andromeda will merge into Milkdromeda, and over the future billions of years, will continue to gather up new galaxies, extract their black holes and mashing them into the collective.

Black holes can absolutely collide. Einstein predicted the gravitational waves this would generate, and now LIGO has observed them for the first time. As better tools are developed, we should learn more and more about these extreme events.

## Death by primordial black hole

Most of the matter in the universe is dark, and despite searches for signatures of related elementary particles on the sky or in laboratory experiments, none were found so far. Primordial black holes (PBHs) could potentially make the dark matter. Various astrophysical constraints rule out PBHs as the dark matter if they have either low or high masses, but allow for a range of masses between a billionth and a thousandth of the mass of the moon—similar to asteroids with a size ranging between one and a hundred miles. Sixty-six million years ago, an asteroid in this size range impacted the Earth and killed the dinosaurs as well as three quarters of all life forms. This is a sober reminder that even the sky is a source of risks. We could protect ourselves from future asteroid impacts by searching for reflected sunlight from their surfaces upon their approach to Earth. In 2005, the U.S. Congress tasked NASA to find 90 percent of all hazardous objects larger than 140 meters, about a hundred times below the size of the Chicxulub impactor that killed the dinosaurs.

This led to the construction of survey telescopes like Pan STARRS and the forthcoming Vera C. Rubin Observatory, which can fulfil two thirds of the congressional goal. These surveys take advantage of the sun as a lamppost that illuminates the dark space near us. An early alert would allow us to deflect dangerous asteroids away from Earth. But PBHs do not reflect sunlight and cannot be identified this way ahead of impact. They do glow faintly in Hawking radiation, but their luminosity is lower than a mini light bulb of 0.1 watt for masses above a millionth of the mass of the moon. Is this invisibility a reason for concern? One would naively expect that such a small object passing through our body would only result in a minor injury confined to a limited cylindrical trail of microscopic width. This would be the case for an energetic particle, like a cosmic ray, passing like a miniature projectile through our body. But this expectation ignores the long-range influence of gravity. The attractive gravitational force induced by a PBH of the abovementioned mass would shrink our entire body by several inches during its quick passage. The pull would be impulsive, lasting 10 microseconds for the typical PBH speed of 100 miles per second in the dark matter halo of the Milky Way galaxy. The resulting pain would feel as if a tiny vacuum cleaner with a tremendous suction power went quickly through our body and shrunk its mussels, bones, blood vessels and internal organs. The dramatic bodily distortion would create severe damage and cause immediate death. How likely is it for us to experience a fatal event of this type during our life?

To illustrate, I will focus on the upper end of the allowed mass window, at which the dark matter is made of PBHs with a thousandth of the mass of the moon. Smaller PBHs could be more common, but their effect is weaker. The horizon size of such a PBH is merely a thousand times larger than the size of an atom. Gladly, a back-of-the-envelope estimate relieves all worries. If PBHs of the above mass make the dark matter, the chance of a PBH passing through our body during our entire lifetime is miniscule, only one part in 1026. This translates to a small probability of order 10–16 for a single death in the entire population of eight billion people living on Earth at present. The likelihood of one death increases to 10–9 if the current population size persists for another billion years, after which the expanding sun is expected to boil off all oceans on Earth. And if we assume similar statistics concerning stars within other galaxies, then only up to a trillion people in the entire observable volume of the universe might be killed by the passage of PBHs through their bodies. It is extremely safe to assume that any of us will not be one of these people. The total number of deaths might be larger in the multiverse if it contains many more volumes with similar conditions, and if even more dangerous types of dark matter exist in parts of it.

Let me explain. In particular, if PBHs in the allowed mass range make up the dark matter, one may wonder whether they pose a threat to our life. An encounter of a PBH with a human body would represent a collision of an invisible relic from the first femtosecond after the big bang with an intelligent body—a pinnacle of complex chemistry made 13.8 billion years later. Although this constitutes a meeting of an extraordinary kind between the early and late universe, we would not wish it upon ourselves.

Obviously, the risks for life on Earth from other catastrophes like asteroid impacts are far greater as the dinosaurs learned from firsthand experience. The above numbers imply that we should not lose sleep or upgrade our medical insurance coverage over concerns about invisible PBHs that may be lurking in the Milky Way’s halo. During these days of looming risks from pandemics and climate change, this is a refreshingly positive message from Mother Nature that we should happily embrace. Nevertheless, it is possible that rare, invisible objects in the outskirts of the solar system, like the hypothesized Planet Nine, are PBHs. In a recent paper that I wrote with my student Amir Siraj, we showed that PBHs could be detected with the Vera C. Rubin Observatory throughout the entire solar system by the flares they generate when they encounter rocks from the Oort cloud.

## Could Primordial Black Holes Deflect Asteriods on a Collision Course with Earth?

Primordial black holes (PBHs) are getting mischievous again. These artefacts from the Big Bang could be responsible for hiding inside planets or stars, they may even punch a neat, radioactive hole through the Earth. Now, they might start playing interplanetary billiards with asteroids in our solar system.

Knocking around lumps of rock may not sound very threatening when compared with the small black holes’ other accolades, but what if a large asteroid was knocked off course and sent in our direction? This could be one of the most catastrophic events yet to come from a PBH passing through our cosmic neighborhood…

As a race, we are constantly worried about the threat of asteroids hitting Earth. What if another large asteroid – like the one that possibly killed the dinosaurs around 65 million BC or the one that blew up over Tunguska in 1908 – were to come hurtling through space and smash into the Earth? The damage caused by such an impact could devastate whole nations, or plunge the world as we know it to the brink of extinction.

But help is at hand. From the combined efforts by groups such as NASAs Near Earth Object Program and international initiatives, governments and institutions are beginning to take this threat seriously. Tracking threatening Near Earth Asteroids is a science in itself, and for now at least, we can relax. There are no massive lumps of rock coming our way (that we know of). The last scare was a comparatively small asteroid called � CT1” which came within 135,000 km of the Earth (about a third of the distance to the Moon) on February 5th, but there are no others forecast for some time.

So, we now have NEO monitoring down to a fine art – we are able to track and calculate the trajectory of observed asteroids throughout the solar system to a very high degree of accuracy. But what would happen if an asteroid should suddenly change direction? This shouldn’t happen right? Think again.

A researcher from the Astro Space Center of the P. N. Lebedev Physics Institute in Moscow has published works focusing on the possibility of asteroids veering off course. And the cause? Primordial black holes. There seems to be many publications out there at the moment musing what would happen should these black holes exist. If they do exist (and there is a high theoretical possibility that they do), there’s likely to be lots of them. So Alexander Shatskiy has gotten to the task of working out the probability of a PBH passing through the solar systems asteroid belts, possibly kicking an asteroid or two across Earths orbit.

Shatskiy finds that PBHs of certain masses are able to significantly change an asteroids orbit. There are estimates of just how big these PBHs can be, the lower limit is set by black hole radiation parameters (as theorized by Stephen Hawking), having little gravitational effect, and the upper limit is estimated to be as massive as the Earth (with an event horizon radius of an inch or so – golf ball size!). Naturally, the gravitational influence by the latter will be massive, greatly affecting any piece of rock as it passes by.

Should PBHs exist, the probability of finding one passing though the solar system will actually be quite high. But what is the probability of the PBH gravitationally scattering asteroids as it passes? If one assumes a PBH with a mass corresponding to the upper mass estimate (i.e. the mass of the Earth), the effect of local space would be huge. As can be seen from an asteroid map (pictured), there is a lot of rocky debris out there! So something with the mass of the Earth barrelling through and scattering an asteroid belt could have severe consequences for planets nearby.

Although this research seems pretty far-fetched, one of the calculations estimate the average periodicity of a large gravitationally disturbed asteroids falling to Earth should occur every 190 million years. According to geological studies, this estimate is approximately the same.

Shatskiy concludes that should small black holes cause deflection of asteroid orbits, perhaps our method of tracking asteroids may be outdated:

If the hypothesis analyzed in this paper is correct, modern methods aimed at averting the asteroid danger appear to be inefficient. This is related to the fact that their main idea is revealing big meteors and asteroids with dangerous orbits and, then, monitoring these bodies. However, if the main danger consists in abrupt changes of asteroidal orbits (because of scattering on a PBH), revealing potentially dangerous bodies is hardly possible.”

## 1 Answer 1

I think, Kyle's link is a really good answer.

For they layman (like me), you can run some numbers here:

a 1 earth mass black-hole (about the size of a ping-pong ball) would radiate so little energy that it would easily destroy the earth, even from a low orbit. It might take some time to devour it, but no question, it would destroy and eat the earth.

a black hole about 1/2 the mass of the moon (this would have the size of a small grain of sand, about 1/10th of a MM in diameter), this would be about temperature stable in the backround radiation of the universe, it would add as much energy as it would radiate off, but on earth, it would see much higher temperatures and would add mass, and in time, devour the earth.

But we'd see the effects long before then. A black hole, 1/2 the mass of the moon would exert 3 G forces at 300 KM, so that that means is it would effectively tear apart an Arizona sized hole, 300 KM deep, wherever it was - now it wouldn't eat that matter right away, but it would pull it apart. Deeper in the earth the effect would be smaller, but the hole would move around with relative ease, basically tearing apart the earth as it moved.

If we look at something more manageable, say, G-force would be 1 G and 1 meter, so it would only be very locally disruptive, like if that fell on your house it would tear a hole through it, but could leave most of the house standing. A 1.5E11 KG black hole, about the mass of 50 empire state buildings. A black hole like this would radiate significant heat, temperature nearly a trillion Kelvin (link above), but passing through the earth it might absorb about as much as it gave off - that's kind of a ballpark guess. Something around that size, in the range of a 150 billion KG. A black hole that size would have a life of about 8 billion years in empty space, and it might be able to eat the earth if it was on the surface/in the core.

I think, somewhere roughly in that range. It's worth pointing out that a black hole that size, it it was in space, it would likely just fly through the earth, not got caught in the earth's gravity and the damage would be far less.

Also, they don't think primordial black holes exist. They've given up the search.

Finally, where it appeared wouldn't matter as much as what it's orbit was. Inside the earth it would interact with more matter than in the atmosphere. Theoretically a black hole in the atmosphere but at orbital speed, could stay in a stable atmospheric orbit for some time. In orbit, far enough away from the earth so it wouldn't absorb earth matter, there would still be potential tidal issues. A moon mass black hole in orbit, 10 times closer than the moon (24,000 miles) would have 100 times the tidal effects than the moon currently has - the oceans would rise and fall about a couple hundred feet with each orbit. At 24,000 miles it would be close to a geosynchronous speed, so you'd only see the high tide every 5 days or so, but that much tidal force might make the earth close to unlivable. Earthquakes and Weather changes.

## Monumental Collision of “Impossible” Black Holes Detected for the First Time

The most massive black hole collision ever detected has been directly observed by the LIGO and VIRGO Scientific Collaboration, which includes scientists from The Australian National University (ANU).

The short gravitational wave signal, GW190521, captured by the LIGO and Virgo gravitational wave observatories in the United States and Europe on May 21 last year, came from two highly spinning, mammoth black holes weighing in at a massive 85 times and 66 times the mass of the Sun, respectively.

But that is not the only reason this system is very special. The larger of the two black holes is considered “impossible.” Astronomers predict that stars between 65 – 130 times the mass of the Sun undergo a process called pair instability, resulting in the star being blown apart, leaving nothing behind.

With a mass of 85 solar masses, the larger black hole falls squarely in that forbidden range, referred to as the upper black hole mass gap, and should be “impossible.” So if it wasn’t created by the collapse of a star, how did it form?

“We think of black holes as the vacuum cleaners of the Universe. They suck in everything in their paths, including gas clouds and stars,” said Professor Susan Scott from the ANU Research School of Physics, a co-author on the publication.

“They also suck in other black holes and it is possible to produce bigger and bigger black holes by the ongoing collisions of earlier generations of black holes. The heavier impossible’ black hole in our detected collision may have been produced in this way.”

The two black holes merged when the Universe was only about seven billion years old, which is roughly half its present age. They formed an even larger black hole weighing a whopping 142 times the mass of the Sun, by far the largest black hole ever observed through gravitational-wave observations.

Black holes of mass 100 to 100,000 solar masses are called intermediate mass black holes (IMBHs). They are heavier than stellar mass black holes but lighter than supermassive black holes often located at the centers of galaxies. There have been no conclusive electromagnetic observations for IMBHs in the mass range 100 to 1,000 solar masses.

“The impossible’ black hole formed by the collision lies in the black hole desert between 100 and 1,000 times the mass of the Sun,” Professor Scott, who is also the Chief Investigator with the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), said.

“We are very excited to have achieved the first direct observation of an IMBH in this mass range. We also saw how it formed, confirming that IMBHs can be produced through the merger of two smaller black holes.”

Another recent study suggests scientists using Caltech’s Zwicky Transient Facility may have spotted a light flare from the collision. This is surprising, as black holes and their mergers are normally dark to telescopes. One theory is the system may have been orbiting a supermassive black hole. The newly formed black hole may have received a kick from the collision, shooting off in a new direction and surging through the disk of gas surrounding the supermassive black hole, causing it to light up. While it is unlikely that the GW190521 detection originated from the same event as the flare, researchers say the possibility that it might have been is intriguing.

“There are a number of different environments in which this system of two black holes could have formed, and the disk of gas surrounding a supermassive black hole is certainly one of them,” OzGrav postdoctoral researcher, Dr. Vaishali Adya from ANU, said.

“But it is also possible that this system consisted of two primordial black holes that formed in the early Universe.

“Every observation we make of two black holes colliding gives us new and surprising information about the lives of black holes throughout the Universe. We are beginning to populate the black hole mass gaps previously thought to exist, with `impossible’ black holes that have been revealed through our detections.”

“GW190521: A Binary Black Hole Merger with a Total Mass of 150 M⊙” by R. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration), 2 September 2020, Physical Review Letters.
DOI: 10.1103/PhysRevLett.125.101102

“Properties and Astrophysical Implications of the 150 Solar Mass Binary Black Hole Merger GW190521” by R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, K. Ackley, C. Adams, R. X. Adhikari, V. B. Adya, C. Affeldt, M. Agathos … and LIGO Scientific Collaboration and Virgo Collaboration, 2 September 2020, Astrophysical Journal Letters.
DOI: 10.3847/2041-8213/aba493

## Black hole, star collisions may illuminate universe's dark side

Scientists looking to capture evidence of dark matter -- the invisible substance thought to constitute much of the universe -- may find a helpful tool in the recent work of researchers from Princeton University and New York University.

The team unveiled in a report in the journal Physical Review Letters this month a ready-made method for detecting the collision of stars with an elusive type of black hole that is on the short list of objects believed to make up dark matter. Such a discovery could serve as observable proof of dark matter and provide a much deeper understanding of the universe's inner workings.

Postdoctoral researchers Shravan Hanasoge of Princeton's Department of Geosciences and Michael Kesden of NYU's Center for Cosmology and Particle Physics simulated the visible result of a primordial black hole passing through a star. Theoretical remnants of the Big Bang, primordial black holes possess the properties of dark matter and are one of various cosmic objects thought to be the source of the mysterious substance, but they have yet to be observed.

If primordial black holes are the source of dark matter, the sheer number of stars in the Milky Way galaxy -- roughly 100 billion -- makes an encounter inevitable, the authors report. Unlike larger black holes, a primordial black hole would not "swallow" the star, but cause noticeable vibrations on the star's surface as it passes through.

Thus, as the number of telescopes and satellites probing distant stars in the Milky Way increases, so do the chances to observe a primordial black hole as it slides harmlessly through one of the galaxy's billions of stars, Hanasoge said. The computer model developed by Hanasoge and Kesden can be used with these current solar-observation techniques to offer a more precise method for detecting primordial black holes than existing tools.

"If astronomers were just looking at the sun, the chances of observing a primordial black hole are not likely, but people are now looking at thousands of stars," Hanasoge said.

"There's a larger question of what constitutes dark matter, and if a primordial black hole were found it would fit all the parameters -- they have mass and force so they directly influence other objects in the universe, and they don't interact with light. Identifying one would have profound implications for our understanding of the early universe and dark matter."

Although dark matter has not been observed directly, galaxies are thought to reside in extended dark-matter halos based on documented gravitational effects of these halos on galaxies' visible stars and gas. Like other proposed dark-matter candidates, primordial black holes are difficult to detect because they neither emit nor absorb light, stealthily traversing the universe with only subtle gravitational effects on nearby objects.

Because primordial black holes are heavier than other dark-matter candidates, however, their interaction with stars would be detectable by existing and future stellar observatories , Kesden said. When crossing paths with a star, a primordial black hole's gravity would squeeze the star, and then, once the black hole passed through, cause the star's surface to ripple as it snaps back into place.

"If you imagine poking a water balloon and watching the water ripple inside, that's similar to how a star's surface appears," Kesden said. "By looking at how a star's surface moves, you can figure out what's going on inside. If a black hole goes through, you can see the surface vibrate."

Eyeing the sun's surface for hints of dark matter

Kesden and Hanasoge used the sun as a model to calculate the effect of a primordial black hole on a star's surface. Kesden, whose research includes black holes and dark matter, calculated the masses of a primordial black hole, as well as the likely trajectory of the object through the sun. Hanasoge, who studies seismology in the sun, Earth and stars, worked out the black hole's vibrational effect on the sun's surface.

Video simulations of the researchers' calculations were created by NASA's Tim Sandstrom using the Pleiades supercomputer at the agency's Ames Research Center in California. One clip shows the vibrations of the sun's surface as a primordial black hole -- represented by a white trail -- passes through its interior. A second movie portrays the result of a black hole grazing the Sun's surface.

Marc Kamionkowski, a professor of physics and astronomy at Johns Hopkins University, said that the work serves as a toolkit for detecting primordial black holes, as Hanasoge and Kesden have provided a thorough and accurate method that takes advantage of existing solar observations. A theoretical physicist well known for his work with large-scale structures and the universe's early history, Kamionkowski had no role in the project, but is familiar with it.

"It's been known that as a primordial black hole went by a star, it would have an effect, but this is the first time we have calculations that are numerically precise," Kamionkowski said.

"This is a clever idea that takes advantage of observations and measurements already made by solar physics. It's like someone calling you to say there might be a million dollars under your front doormat. If it turns out to not be true, it cost you nothing to look. In this case, there might be dark matter in the data sets astronomers already have, so why not look?"

One significant aspect of Kesden and Hanasoge's technique, Kamionkowski said, is that it narrows a significant gap in the mass that can be detected by existing methods of trolling for primordial black holes .

The search for primordial black holes has thus far been limited to masses too small to include a black hole, or so large that "those black holes would have disrupted galaxies in heinous ways we would have noticed," Kamionkowski said. "Primordial black holes have been somewhat neglected and I think that's because there has not been a single, well-motivated idea of how to find them within the range in which they could likely exist."

The current mass range in which primordial black holes could be observed was set based on previous direct observations of Hawking radiation -- the emissions from black holes as they evaporate into gamma rays -- as well as of the bending of light around large stellar objects, Kesden said. The difference in mass between those phenomena, however, is enormous, even in astronomical terms. Hawking radiation can only be observed if the evaporating black hole's mass is less than 100 quadrillion grams. On the other end, an object must be larger than 100 septillion (24 zeroes) grams for light to visibly bend around it. The search for primordial black holes covered a swath of mass that spans a factor of 1 billion, Kesden explained -- similar to searching for an unknown object with a weight somewhere between that of a penny and a mining dump truck .

He and Hanasoge suggest a technique to give that range a much-needed trim and established more specific parameters for spotting a primordial black hole. The pair found through their simulations that a primordial black hole larger than 1 sextillion (21 zeroes) grams -- roughly the mass of an asteroid -- would produce a noticeable effect on a star's surface.

"Now that we know primordial black holes can produce detectable vibrations in stars, we could try to look at a larger sample of stars than just our own sun," Kesden said.

"The Milky Way has 100 billion stars, so about 10,000 detectable events should be happening every year in our galaxy if we just knew where to look."

This research was funded by grants from NASA and by the James Arthur Postdoctoral Fellowship at New York University.

## Black hole, star collisions may illuminate universe's dark side

Scientists looking to capture evidence of dark matter -- the invisible substance thought to constitute much of the universe -- may find a helpful tool in the recent work of researchers from Princeton University and New York University.

The team unveiled in a report in the journal Physical Review Letters this month a ready-made method for detecting the collision of stars with an elusive type of black hole that is on the short list of objects believed to make up dark matter. Such a discovery could serve as observable proof of dark matter and provide a much deeper understanding of the universe's inner workings.

Postdoctoral researchers Shravan Hanasoge of Princeton's Department of Geosciences and Michael Kesden of NYU's Center for Cosmology and Particle Physics simulated the visible result of a primordial black hole passing through a star. Theoretical remnants of the Big Bang, primordial black holes possess the properties of dark matter and are one of various cosmic objects thought to be the source of the mysterious substance, but they have yet to be observed.

If primordial black holes are the source of dark matter, the sheer number of stars in the Milky Way galaxy -- roughly 100 billion -- makes an encounter inevitable, the authors report. Unlike larger black holes, a primordial black hole would not "swallow" the star, but cause noticeable vibrations on the star's surface as it passes through.

Thus, as the number of telescopes and satellites probing distant stars in the Milky Way increases, so do the chances to observe a primordial black hole as it slides harmlessly through one of the galaxy's billions of stars, Hanasoge said. The computer model developed by Hanasoge and Kesden can be used with these current solar-observation techniques to offer a more precise method for detecting primordial black holes than existing tools.

"If astronomers were just looking at the sun, the chances of observing a primordial black hole are not likely, but people are now looking at thousands of stars," Hanasoge said.

"There's a larger question of what constitutes dark matter, and if a primordial black hole were found it would fit all the parameters -- they have mass and force so they directly influence other objects in the universe, and they don't interact with light. Identifying one would have profound implications for our understanding of the early universe and dark matter."

Although dark matter has not been observed directly, galaxies are thought to reside in extended dark-matter halos based on documented gravitational effects of these halos on galaxies' visible stars and gas. Like other proposed dark-matter candidates, primordial black holes are difficult to detect because they neither emit nor absorb light, stealthily traversing the universe with only subtle gravitational effects on nearby objects.

Because primordial black holes are heavier than other dark-matter candidates, however, their interaction with stars would be detectable by existing and future stellar observatories , Kesden said. When crossing paths with a star, a primordial black hole's gravity would squeeze the star, and then, once the black hole passed through, cause the star's surface to ripple as it snaps back into place.

"If you imagine poking a water balloon and watching the water ripple inside, that's similar to how a star's surface appears," Kesden said. "By looking at how a star's surface moves, you can figure out what's going on inside. If a black hole goes through, you can see the surface vibrate."

Eyeing the sun's surface for hints of dark matter

Kesden and Hanasoge used the sun as a model to calculate the effect of a primordial black hole on a star's surface. Kesden, whose research includes black holes and dark matter, calculated the masses of a primordial black hole, as well as the likely trajectory of the object through the sun. Hanasoge, who studies seismology in the sun, Earth and stars, worked out the black hole's vibrational effect on the sun's surface.

Video simulations of the researchers' calculations were created by NASA's Tim Sandstrom using the Pleiades supercomputer at the agency's Ames Research Center in California. One clip shows the vibrations of the sun's surface as a primordial black hole -- represented by a white trail -- passes through its interior. A second movie portrays the result of a black hole grazing the Sun's surface.

Marc Kamionkowski, a professor of physics and astronomy at Johns Hopkins University, said that the work serves as a toolkit for detecting primordial black holes, as Hanasoge and Kesden have provided a thorough and accurate method that takes advantage of existing solar observations. A theoretical physicist well known for his work with large-scale structures and the universe's early history, Kamionkowski had no role in the project, but is familiar with it.

"It's been known that as a primordial black hole went by a star, it would have an effect, but this is the first time we have calculations that are numerically precise," Kamionkowski said.

"This is a clever idea that takes advantage of observations and measurements already made by solar physics. It's like someone calling you to say there might be a million dollars under your front doormat. If it turns out to not be true, it cost you nothing to look. In this case, there might be dark matter in the data sets astronomers already have, so why not look?"

One significant aspect of Kesden and Hanasoge's technique, Kamionkowski said, is that it narrows a significant gap in the mass that can be detected by existing methods of trolling for primordial black holes .

The search for primordial black holes has thus far been limited to masses too small to include a black hole, or so large that "those black holes would have disrupted galaxies in heinous ways we would have noticed," Kamionkowski said. "Primordial black holes have been somewhat neglected and I think that's because there has not been a single, well-motivated idea of how to find them within the range in which they could likely exist."

The current mass range in which primordial black holes could be observed was set based on previous direct observations of Hawking radiation -- the emissions from black holes as they evaporate into gamma rays -- as well as of the bending of light around large stellar objects, Kesden said. The difference in mass between those phenomena, however, is enormous, even in astronomical terms. Hawking radiation can only be observed if the evaporating black hole's mass is less than 100 quadrillion grams. On the other end, an object must be larger than 100 septillion (24 zeroes) grams for light to visibly bend around it. The search for primordial black holes covered a swath of mass that spans a factor of 1 billion, Kesden explained -- similar to searching for an unknown object with a weight somewhere between that of a penny and a mining dump truck .

He and Hanasoge suggest a technique to give that range a much-needed trim and established more specific parameters for spotting a primordial black hole. The pair found through their simulations that a primordial black hole larger than 1 sextillion (21 zeroes) grams -- roughly the mass of an asteroid -- would produce a noticeable effect on a star's surface.

"Now that we know primordial black holes can produce detectable vibrations in stars, we could try to look at a larger sample of stars than just our own sun," Kesden said.

"The Milky Way has 100 billion stars, so about 10,000 detectable events should be happening every year in our galaxy if we just knew where to look."

This research was funded by grants from NASA and by the James Arthur Postdoctoral Fellowship at New York University.

## Are they’re any black holes that will collide with earth within our lifetimes?

None that we know about as stellar-mass black holes are notoriously difficult to locate. To put your mind at ease, however, think of it this way. In it's 4.5 billion year history, the Earth has been literally bombarded with asteroids and comets. On average, we get a decent sized air-burster about every 15 months. Something large enough to take out a city happens around every 5000 years or so. Something large enough to really devastate the entire planet happens one every 150-200 million years or so.

But in all that time, in all 4.5 BILLION years of the planet's history, no black hole has ever crossed our path. If it had, we wouldn't be here.

#### Helio

Fortunately, the nearest black hole is about 7 thousand trillion miles away and it's not coming directly towards us.

Alpha Centauri is coming towards us but it won't be a very close pass. Its closest point to us will be about 3.23 lyrs (

18 trillion miles), which won't happen until about another

#### Ybs_itsurboi

Fortunately, the nearest black hole is about 7 thousand trillion miles away and it's not coming directly towards us.

Alpha Centauri is coming towards us but it won't be a very close pass. Its closest point to us will be about 3.23 lyrs (

18 trillion miles), which won't happen until about another

#### Dfjchem721

Clearly the science of black holes is still evolving. That BHs are restricted to stellar collapse necessarily assumes they cannot form in any other way. It has been suggested that micro BHs could be formed with the LHC, and consume the earth. (This is not equivalent to the atmosphere igniting during the first nuclear detonation in 1945.) Certainly sounds ludicrous, and probably is. For a long time, black holes seemed ludicrous themselves. Hawking himself doubted their existence, but later changed his tune - from soft rock to hard metal! The doubter became the biggest adherent! Many examples of such things in science.

All known BHs were detected due to their gravitational effects on objects near them - i.e. objects that we can observe since you cannot "see" a BH. This puts severe constraints on establishing firm aspects of their distribution, etc.

In reality, too little is known about them to be certain of their size and density in the universe.

For an interesting concept largely considered nonsense by most of the "certain" folks in cosmology, try this one on for size:

### Primordial black hole - Wikipedia

Stirring up the pot can often yield superior results! And those inside boxes with no windows can miss things of significance.

Before 1938, all the great minds in physics believed that fission was impossible, until radiochemist Otto Hahn proved they were wrong. How could all those brilliant minds have been so wrong? They were very clever people. Sometimes when you get too close to things you cannot see alternatives, indeed, some that might be right in front of your nose!

#### Dfjchem721

Here in another of those hair-brained ideas on Primordial Black Holes (PBHs). There are a number of high brows out there who insist they are possible, indeed some are sure of it! One of many nice things about them is they are a known component in the universe, and do not rely on exotic new "objects", etc.

Check this out - it relates to mergers resulting in gravitational waves:

### Did Astronomers Just Discover Black Holes from the Big Bang?

www.scientificamerican.com

Black hole mergers have revised interest in one of my favorite hypotheses. This is due in part to notions of prior "constraints". Stating firm constraints can lead one to erroneous assumptions and conclusions since locking into constraints locks one out of alternative thinking.

There is some rising anxiety among the anti-PBH die-hards. Careers are at stake here, and egos even more so.

Yes, SciAmer has published trash in the past. But they are far from alone in that! And this might actually be right, and would constrain the "trash" to hypotheticals at best. As the story notes, "only time and more data will tell."

I tend contrarian when everyone is saying "it has to be this way" and there are rational alternatives not well investigated. There is no fun in jumping on a scientific band-wagon. Also have admitted to knowing enough to be dangerous!

#### Ybs_itsurboi

Here in another of those hair-brained ideas on Primordial Black Holes (PBHs). There are a number of high brows out there who insist they are possible, indeed some are sure of it! One of many nice things about them is they are a known component in the universe, and do not rely on exotic new "objects", etc.

Check this out - it relates to mergers resulting in gravitational waves:

### Did Astronomers Just Discover Black Holes from the Big Bang?

www.scientificamerican.com

Black hole mergers have revised interest in one of my favorite hypotheses. This is due in part to notions of prior "constraints". Stating firm constraints can lead one to erroneous assumptions and conclusions since locking into constraints locks one out of alternative thinking.

There is some rising anxiety among the anti-PBH die-hards. Careers are at stake here, and egos even more so.

Yes, SciAmer has published trash in the past. But they are far from alone in that! And this might actually be right, and would constrain the "trash" to hypotheticals at best. As the story notes, "only time and more data will tell."

I tend contrarian when everyone is saying "it has to be this way" and there are rational alternative not well investigated. There is no fun in jumping on a scientific band-wagon. Also have admitted to knowing enough to be dangerous!

#### Dfjchem721

If there is, we will likely never know it. Unlike a comet, you would never see it coming. If one consumed the earth, we would disappear in almost an instant. That would be a case where human science meets its ultimate constraint!

Again, as the story notes: "only time and more data will tell."

#### Dfjchem721

In reconsidering a potential encounter with a hypothetical black hole making a fatal hit on earth, our ability to detect it ahead of time seems largely dependent on the BH size and closing "velocity" of the encounter. Assuming that this encounter remains relatively slow, than the ability to detect it ahead of time would seem to depend entirely on its mass, and, simplistically, the true extent of the most distant objects still orbiting the earth, assuming they have sufficient mass to emit some kind of "signal" when disappearing into the BH. So this all depends on the closing speed and BH mass (and mostly Newtonian physics).

That signal might be as simple as the mysterious disappearance from a specific region in the sky of various objects in the Kuiper Belt that are periodically tracked. One might suppose if a large enough black hole approaches very slowly, it would begin to consume outer components of the solar system as it made its way to earth. Not being an expert on BH "matter acquisition" physics, some or all of these disappearances might result in a brief gamma ray/x-ray burst, or perhaps some other ER, or nothing but their disappearance.

Surely by the time it ate up a big gas giant, there would be no doubt about what is going on! But this is where my physics breaks down. It seems possible that if Neptune is being consumed, so are we. Still, early detection of some kind would be likely if the closing velocity is slow enough for the "right" sized BH.

But perhaps smaller BHs of some size, say 0.1 solar masses (a PBH), could move through the solar system without much interaction unless something substantial is right in its way. If earth is a dead on hit, one imagines we would disappear in an instant without any warning ahead of time.

Clearly one of the biggest issues to model for a predictable collision with earth is the effect of the intense gravitational field the BH has on objects in the solar system, and even beyond. A super massive black hole approaching the solar system at a fairly slow speed should begin to warp images of objects like stars and galaxies etc, that are directly aligned with it, and perhaps even lens objects behind it!

A deep sky survey might pick that up at some point, possibly months or years before the encounter. Again, it would likely depend largely on BH mass and closing speed. Of course most of this is based on Newtonian physics, but it seems, with the exception of mass consumption by the BH, that is mostly what it is. At least it is the best I can do, with the help of Sir Isaac, and a whole lot of modern science, and certainly the "conjecture".