# View from inside the black hole

If an observer is falling toward a black hole with its face away from singularity then what will he observe after crossing the event horizon? The reason that why I am asking this question because as far as I know for an outside observer, the falling observer appear to freeze at event horizon i.e. time appear to stop for falling observer. So if the falling observer is able to look outward after crossing event horizon then he will be able to see an infinite amount of time which is impossible. So what will the observer see after crossing the event horizon?

The external observer's view does not imply anything about an observer within the event horizon.

The event horizon itself is just an indicator of the edge of the region where light can no longer escape. Light can head inwards as you would expect.

So an observer inside the event horizon will be able to see light reaching them as normal (well, not exactly as normal, as there will be lensing effects) - there will not be an infinite amount of time visible.

If an observer is falling toward a black hole with his face away from singularity then what will he observe after crossing the event horizon?

Nothing.

The reason that why I am asking this question because as far as I know for an outside observer, the falling observer appears to freeze at the event horizon i.e. time appears to stop for the falling observer.

Correct. Gravitational time dilation goes infinite, and the distant observer says the "coordinate" speed of light at the event horizon is zero.

So if the falling observer is able to look outward after crossing the event horizon then he will be able to see an infinite amount of time which is impossible. So what will the observer see after crossing the event horizon?

Nothing. The coordinate speed of light is zero at that location, which means that by our clocks, it takes forever to see anything. So the falling observer hasn't seen anything yet, and he never ever will.

IMHO it's worth reading the mathspages Formation and Growth of Black Holes and paying attention to the frozen star interpretation:

"Incidentally, we should perhaps qualify our dismissal of the 'frozen star' interpretation, because it does (arguably) give a servicable account of phenomena outside the event horizon, at least for an eternal static configuration. Historically the two most common conceptual models for general relativity have been the "geometric interpretation" (as originally conceived by Einstein) and the "field interpretation" (patterned after the quantum field theories of the other fundamental interactions). These two views are operationally equivalent outside event horizons, but they tend to lead to different conceptions of the limit of gravitational collapse. According to the field interpretation, a clock runs increasingly slowly as it approaches the event horizon (due to the strength of the field), and the natural "limit" of this process is that the clock asymptotically approaches "full stop" (i.e., running at a rate of zero). It continues to exist for the rest of time, but it's "frozen" due to the strength of the gravitational field. Within this conceptual framework there's nothing more to be said about the clock's existence… "

The author doesn't favour it, but it squares with what Einstein said about the speed of light varying with gravitational potential. The other interpretation doesn't. And note that Einstein didn't refer to the "coordinate" speed of light. He simply referred to the speed of light. So we can reasonably say that at the event horizon, the speed of light is zero, and that this is why a vertical light beam can't get out. The distant observer sees the infalling observer freeze at the event horizon. But the infalling observer doesn't see himself as frozen, because the speed of light at that location is zero. He sees nothing.

NB: SR time dilation is symmetrical, but GR time dilation isn't. If you and I passed each other in gravity-free space at some relativistic speed, we would each claim that the other's clock was slower. But when we're at different elevations, we both agree that the lower clock is going slower.

For the observer, they would see the person falling into the black hole almost in slow motion as their body seemed to stretch itself because of light distortions from the immense gravitational pull of the black hole. When you reach the horizon, the observer would see your body "freeze" and then slowly disappear, almost fading away.

For you, the person falling in, you would either see your body stretching like silly puddy or falling normally depending on the size of the black hole. You would then fall normally until you reached the singularity.

This is all theoretical of course

BBC The strange fate of a person falling into a black hole

Let's take the case we enter $mathrm{BH}_mathrm{Sgr,A^*}$ (the super-massive black hole at the center of the way) backwards; from what I understood here, an external observer should experience you slowing down, whereas you will see is time accelerate.

If you had the possibility to "hover" at 1 meter from the surface, you would see time be accelerated a million time for ordinary mater in low-gravity fields (see calculation at earlier reference), and more and more the closer you get to the boundary.

Then once you pass the border, I recon you should see yourself in the first place, because photons you emit will be dragged back to the black hole by its gravity!! I guess it requires you enter the black hole with a specific trajectory to compensate rotational effects. But since other light should also be entering the BH, it should superpose to yours…

Anyway, there is a limit to the amount of light that enters the BH: its the rate at which BH grows: if light entering BH would be infinite, then BH mass should become infinite as soon as the BH becomes a BH.

## What Would the View Be Like From Within a Black Hole?

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If you fell into a black hole, would you be engulfed in darkness? Could you see out beyond the event horizon? Are there wormholes inside black holes? Do black holes give birth to baby universes? Believe it or not, these questions may have been answered. Andrew Hamilton from the University of Colorado and Gavin Polhemus have created a video showing what falling into a Schwarzschild black hole might look like to the person falling in. The two researchers warn that based on our experience in the 3D world, we might imagine that falling through the horizon would be like falling through any other surface. However, they say, it’s not. And likely, a person falling into the black hole would be able to see outside of the event horizon.

“When an observer outside the horizon observes the horizon of a black hole,” the researchers say, “they are actually observing the outgoing horizon. When they subsequently fall through the horizon, they do not fall through the horizon they were looking at, the outgoing horizon rather, they fall through the ingoing horizon, which was invisible to them until they actually passed through it. Once inside the horizon, the infaller sees both outgoing and ingoing horizons.”

As you might expect, this work has created a lot of interest, and the servers hosting the videos has already crashed once, but now has been put on a new server. Watch several different videos. along with written commentary here.

While this work is great fun to watch and delve into, it also has great scientific merit. Calculating what the universe looks like from inside a black hole is an important exercise because it forces physicists to examine how the laws of physics behave at a breaking point. For example, near the singularity, the observer’s view in the horizontal plane is highly blueshifted, but all directions other than horizontal appear highly redshifted.

Also, the principle of locality is severely tested inside a black hole. This is the idea that a point in space can only be influenced by its immediate surroundings. But when space is infinitely stretched, as physicists think it is at the heart of a black hole, the concept of “immediate surroundings” doesn’t make sense. So the concept of locality begins to lose its meaning too.

And that provides an interesting “thought laboratory” in which physicists can ask how ideas such as quantum mechanics and relativity might break down.

It also provides some other entertaining results. For example, space is so heavily curved inside a black hole that ordinary binocular vision would be no good for determining distances, says Hamilton. But trinoculars might work.

## Astronomers Capture Best View Yet of a Black Hole Spaghettifying a Star

When black holes slurp up stars, they make a mess on a galactic scale. Now, astronomers have gotten the best look yet at a black hole swallowing a star, called a tidal disruption event. The details were published on October 12 in the Monthly Notices of the Royal Astronomical Society.

In 2019, astronomers at the Zwicky Transient Facility in California saw a flare pop up in a galaxy in the constellation Eridanus, Dennis Overbye reports for the New York Times. A star near the size of our sun had fallen too close to the galaxy’s central black hole, and the intense gravity had begun stretching, squishing and shredding the star into stellar noodles. By the end of the event, months later, the black hole slurped up half of the star’s mass, and the rest was shot out into space.

At only about 215 light-years away, this light lunch provided an unprecedented look into the stages of a star’s spaghettification.

“We were able to capture this event early because it is the nearest tidal disruption event seen to date,” astronomer Edo Berger of the Harvard & Smithsonian Center for Astrophysics tells Smithsonian in an email. “Since the more nearby an object is, the brighter it will appear to be, this allows us to discover such an object well before it reaches its peak brightness.”

Breakthrough research on black holes won three physicists the Nobel Prize this year. The supermassive cosmic phenomena are deep, dark pits in the fabric of space-time first described by Albert Einstein, where the gravity is so strong that at a certain point, nothing can escape its pull.

“If you get close enough to a black hole that you’re within this region called the ‘event horizon’ and you shine a flashlight away from the center of the black hole the light will go towards the center of the black hole,” astrophysicist Katie Mack told Inverse’s Danny Paez in 2018. “…That’s the point of no return because it’s physically impossible to move away from the center of the black hole, all directions are towards [its] center.”

The black hole in the new study is about a million times more massive than the star it consumed, according to a statement. Once the star was within 100 million miles—about the same distance as Earth to our sun—of the black hole, it was doomed. The star gets stretched out into a long stream around the black hole, and when the ends collide, some debris is thrown out into space while the black hole begins to pull the spaghettified star in.

“If you were to picture the sun being stretched into a thin stream and rushing toward us, that’s what the black hole saw.” University of Birmingham astrophysicist Matt Nicholl tells the New York Times.

Because astronomers caught a glimpse of the event early on, they organized a team across the world’s largest and best telescopes and watched the black hole consume the star over the course of six months.

“It seems to have paid off because we really got a great look at this thing,” Nicholl tells Paola Rosa-Aquino at Popular Science. The flare peaked in brightness after about one month, and faded five months later.

“These faster ones are harder to find, so it suggests that there might be a lot of these short-lived flares that have escaped our attention until now,” Nicholl adds to Popular Science.

Astronomers captured the event in x-ray and gamma ray, radio emissions, and visible light images. They found that most of the light came from the wall of dust and debris from the star that surrounded the black hole. The spaghettified star’s collision launched material into space at 6,000 miles per second, per the New York Times. At that speed, something could travel from Earth to the Moon in about 40 seconds.

As astronomers gain access to new, advanced telescopes like the Vera Rubin Observatory, researchers will be scanning the skies with more sensitive equipment. That may enable them to capture more of these star-shredding events early, Berger says.

“We know that most galaxies have supermassive black hole at their centers,” Northwestern University astronomer Kate Alexander wrote in an email to the New York Times. “But we still don’t understand exactly how these black holes grew to be as big as they are, or how they shape their host galaxies.”

## How Black Hole Atoms Could Solve One of Astronomy’s Biggest Problems

Perhaps the greatest problem in astrophysics is the mystery of dark matter. When astronomers observe other galaxies, they can see how fast these objects rotate. They can also see how much visible mass they contain and calculate the gravitational forces it must generate.

And therein lies the problem. The visible matter simply does not generate enough gravity to hold the galaxies together. By this measure, they ought to fly apart.

So astrophysicists believe that something else must be holding the galaxies together. Enter dark matter—some kind of mysterious, invisible stuff that generates the gravity that holds the universe together.

The big question is: what is this stuff? Today, Vyacheslav Dokuchaev and Yury Eroshenko Institute for Nuclear Research of the Russian Academy of Sciences in Moscow propose an interesting new idea.

These guys say that dark matter is composed of black hole atoms—microscopic black holes with a charge that have somehow captured an electron or proton leaving them electrically neutral. “We propose these black hole atoms as the possible origin of dark matter particles,” they say.

Physicists have long thought that microscopic black holes must have formed in the early universe. That’s because quantum fluctuation in the density of matter at this time would have created some regions of space that were dense enough to form black holes.

Some of these would have been huge, perhaps seeding the formation of galaxies. But most would have been much smaller—microscopic, in fact.

The thinking is that today, the universe must be filled with these objects. Various theorists have discussed the possibility that these so-called ‘primordial black holes’ could be the mysterious dark matter.

One problem is the possibility that primordial black holes may have an electric charge. In that case, it’s quite possible that they would have attracted protons or electrons, leaving them electrically neutral, just like atoms.

The question that Dokuchaev and Eroshenko address is what properties such objects would have. And the answer is exactly the properties you’d expect of dark matter.

For a start, black hole atoms would be massive, from 10^14 kilograms to 10^23 kilograms, about the same mass range as asteroids. But even at that mass, they would be tiny: smaller than atoms but larger than nucleons, such as protons and neutrons.

They would also be unlike any other form of matter in the universe. Dokuchaev and Eroshenko calculate, for example, that an electron (or proton) could orbit inside the black hole’s horizon, meaning that it can never escape.

That would also limit the interaction with ordinary matter. So despite their mass, black hole atoms would interact with other matter less strongly than neutrinos. “The interaction of the neutral black hole atoms with ordinary matter via the gravitational dynamical friction effect is extremely weak,” they say.

The bottom line is that black hole atoms are dark, massive, non-interacting particles. “These properties are just one needs for the dark matter candidates,” say Dokuchaev and Eroshenko.

So how to detect them? Not very easily. Dokuchaev and Eroshenko say that the formation of these atoms might produce a measurable signal. When an electron tunnels into a microscopic black hole to form a black hole atom, it ought to release energy in the form of a flash of ultrahigh energy cosmic rays.

What’s more, the electrons may be quantised, just as in ordinary atoms, and the jumps from one level to another would release photons. “This effect makes “black hole atoms” observable in principle,” they say.

That’s an interesting idea. But it has its fair share of problems too.

If black hole atoms are dark matter, then they must fill the universe. Perhaps the most serious problem is finding a way to unambiguously observe these objects and distinguish them from ordinary black holes that are electrically neutral or indeed other proposed candidates for dark matter.

But there are also exciting possibilities too—that black hole atoms might interact with each other in a way that forms molecules and other larger things, for example. Just what structures might form is an open question.

There’s more work here for black hole theorists, should they have a few hours to spare.

Ref: arxiv.org/abs/1403.1375 : Black Hole Atom as A Dark Matter Particle Candidate

## View from inside the black hole - Astronomy

We know that black holes suck in light. So if you were inside a black hole, would it seem incredibly bright, or is the light destroyed/converted somehow as you fall into the black hole? Also, can you see out? The videos we looked at seemed to show that everything turns into a doughtnut shape around you?

We are - Sam, aged eight and mummy aged 37, high school science teacher!!

This is a really interesting question and I have taken some time to think about my answer so I hope that I will get it at least mostly right. Black holes are strange things - completely outside of our normal physical intuition so it can be really hard to think about what things would be like near them! Of course the first thing that I should say is that it would not be possible to go into a black hole and survive long enough to look out. If you were not torn apart by the enormous tidal forces you would be fried by the extremely high energy radiation (X-rays and Gamma-rays) 'raining' down on you. Also between crossing the event horizon and hitting the central singularity is likely to be only a fraction of a second of your time!

That being said, it is interesting to think about what things would look like if we could see them. The first thing that comes to mind is that as the light from the universe "falls" into the black hole it gains energy. This means that its wavelength gets shorter. Blue light has a shorter wavelength than red light - so very simply things would appear to get bluer. There is also light outside the range which we can see (as I'm sure Mummy knows, see also this nice explanation with diagrams ) so the longer wavelength radiation would get shifted into the visible range (and through it) and the visible would get shifted to shorter wavelengths. Eventually at the event horizon there is an infinite shift - so the light has an infinite amount of energy, but zero wavelength. What this would look like I can't even imagine! I'm not sure if you could see it even if you hadn't been killed by the gamma-radiation hitting you as you got close to it!

Now if we assume not only that we haven't died on the way into the black hole, and that we can see the light which has an infinite blue shift we would be able to see some weird things. If we looked away from the singularity at the centre of the black hole we would be able to see the whole universe in one small patch of our sky - even the stuff that is actually behind the singularity! Also time outside would appear to be running much faster, so we would be able to see the evolution of the universe "flash" before our eyes.

It would be pretty interesting I think - although like I said it would seem to be completely impossible to even do and certainly impossible to survive it given that you would then be stuck inside a black hole!

#### Karen Masters

Karen was a graduate student at Cornell from 2000-2005. She went on to work as a researcher in galaxy redshift surveys at Harvard University, and is now on the Faculty at the University of Portsmouth back in her home country of the UK. Her research lately has focused on using the morphology of galaxies to give clues to their formation and evolution. She is the Project Scientist for the Galaxy Zoo project.

## Astronomers find closest black hole to Earth

This artist's impression shows the orbits of the objects in the HR 6819 triple system. This system is made up of an inner binary with one star (orbit in blue) and a newly discovered black hole (orbit in red), as well as a third star in a wider orbit (also in blue).The team originally believed there were only two objects, the two stars, in the system. However, as they analysed their observations, they were stunned when they revealed a third, previously undiscovered body in HR 6819: a black hole, the closest ever found to Earth. The black hole is invisible, but it makes its presence known by its gravitational pull, which forces the luminous inner star into an orbit. The objects in this inner pair have roughly the same mass and circular orbits.The observations, with the FEROS spectrograph on the 2.2-metre telescope at ESO's La Silla, showed that the inner visible star orbits the black hole every 40 days, while the second star is at a large distance from this inner pair. Credit: ESO/L. Calçada

A team of astronomers from the European Southern Observatory (ESO) and other institutes has discovered a black hole lying just 1000 light-years from Earth. The black hole is closer to our Solar System than any other found to date and forms part of a triple system that can be seen with the naked eye. The team found evidence for the invisible object by tracking its two companion stars using the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory in Chile. They say this system could just be the tip of the iceberg, as many more similar black holes could be found in the future.

"We were totally surprised when we realised that this is the first stellar system with a black hole that can be seen with the unaided eye," says Petr Hadrava, Emeritus Scientist at the Academy of Sciences of the Czech Republic in Prague and co-author of the research. Located in the constellation of Telescopium, the system is so close to us that its stars can be viewed from the southern hemisphere on a dark, clear night without binoculars or a telescope. "This system contains the nearest black hole to Earth that we know of," says ESO scientist Thomas Rivinius, who led the study published today in Astronomy & Astrophysics.

The team originally observed the system, called HR 6819, as part of a study of double-star systems. However, as they analysed their observations, they were stunned when they revealed a third, previously undiscovered body in HR 6819: a black hole. The observations with the FEROS spectrograph on the MPG/ESO 2.2-metre telescope at La Silla showed that one of the two visible stars orbits an unseen object every 40 days, while the second star is at a large distance from this inner pair.

Dietrich Baade, Emeritus Astronomer at ESO in Garching and co-author of the study, says: "The observations needed to determine the period of 40 days had to be spread over several months. This was only possible thanks to ESO's pioneering service-observing scheme under which observations are made by ESO staff on behalf of the scientists needing them."

The hidden black hole in HR 6819 is one of the very first stellar-mass black holes found that do not interact violently with their environment and, therefore, appear truly black. But the team could spot its presence and calculate its mass by studying the orbit of the star in the inner pair. "An invisible object with a mass at least 4 times that of the Sun can only be a black hole," concludes Rivinius, who is based in Chile.

Astronomers have spotted only a couple of dozen black holes in our galaxy to date, nearly all of which strongly interact with their environment and make their presence known by releasing powerful X-rays in this interaction. But scientists estimate that, over the Milky Way's lifetime, many more stars collapsed into black holes as they ended their lives. The discovery of a silent, invisible black hole in HR 6819 provides clues about where the many hidden black holes in the Milky Way might be. "There must be hundreds of millions of black holes out there, but we know about only very few. Knowing what to look for should put us in a better position to find them," says Rivinius. Baade adds that finding a black hole in a triple system so close by indicates that we are seeing just "the tip of an exciting iceberg."

Already, astronomers believe their discovery could shine some light on a second system. "We realised that another system, called LB-1, may also be such a triple, though we'd need more observations to say for sure," says Marianne Heida, a postdoctoral fellow at ESO and co-author of the paper. "LB-1 is a bit further away from Earth but still pretty close in astronomical terms, so that means that probably many more of these systems exist. By finding and studying them we can learn a lot about the formation and evolution of those rare stars that begin their lives with more than about 8 times the mass of the Sun and end them in a supernova explosion that leaves behind a black hole."

The discoveries of these triple systems with an inner pair and a distant star could also provide clues about the violent cosmic mergers that release gravitational waves powerful enough to be detected on Earth. Some astronomers believe that the mergers can happen in systems with a similar configuration to HR 6819 or LB-1, but where the inner pair is made up of two black holes or of a black hole and a neutron star. The distant outer object can gravitationally impact the inner pair in such a way that it triggers a merger and the release of gravitational waves. Although HR 6819 and LB-1 have only one black hole and no neutron stars, these systems could help scientists understand how stellar collisions can happen in triple star systems.

This research was presented in the paper "A naked-eye triple system with a nonaccreting black hole in the inner binary", published today in Astronomy & Astrophysics.

## What is a Black Hole Made of?

Question: I googled this question while looking for an answer to something even more vague: what is a black hole made of? If the 3 observable properties or a black hole are supposed to be mass, charge, and angular momentum, then what “inside” the black hole can still provide those properties if all matter in a black hole has supposedly been destroyed? The only thing I’ve been able to imagine is that a black hole does not actually destroy any matter that falls into it … it just prevents us from observing it. Otherwise the implication is that mass, charge, and angular momentum can exist independently of matter. — Rob

Answer: As you already know, black holes are places where extreme gravitational attraction draws everything, even light, to a single point in space. The problem with understanding exactly what happens to the stuff that pulled into a black hole is that physicists really don’t have a complete understanding of how gravity works under the extreme conditions found in a black hole. Called “quantum gravity”, an understanding of how gravity works in a black hole requires physicists to figure out what happens to gravity at atomic-scale levels. The physical properties of a black hole, which as you have said are mass, charge, and angular momentum, are measurable and are properties that derive from the event horizon of the black hole. Inside the event horizon, which is where quantum gravity effects start to come into play, are poorly understood. In the end, your suggestion that matter is not “destroyed” when it enters a black hole but just becomes unobservable to us, is plausible. Physicists cannot be definitive on this issue, though, as we just don’t have a good understanding of how gravity works at the center of a black hole.

## Black Hole Fits Inside Earth’s Orbit

Thirty years after astronomers discovered the mysterious object at the exact center of our Milky Way Galaxy , an international team of scientists has finally succeeded in directly measuring the size of that object, which surrounds a black hole nearly four million times more massive than the Sun. This is the closest telescopic approach to a black hole so far and puts a major frontier of astrophysics within reach of future observations. The scientists used the National Science Foundation’s Very Long Baseline Array (VLBA) radio telescope to make the breakthrough.

“This is a big step forward,” said Geoffrey Bower, of the University of California-Berkeley. “This is something that people have wanted to do for 30 years,” since the Galactic center object, called Sagittarius A* (pronounced “A-star”), was discovered in 1974. The astronomers reported their research in the April 1 edition of Science Express.

“Now we have a size for the object, but the mystery about its exact nature still remains,” Bower added. The next step, he explained, is to learn its shape, “so we can tell if it is jets , a thin disk , or a spherical cloud.”

The Milky Way’s center, 26,000 light-years from Earth, is obscured by dust, so visible-light telescopes cannot study the object. While radio waves from the Galaxy’s central region can penetrate the dust, they are scattered by turbulent charged plasma in the space along the line of sight to Earth. This scattering had frustrated earlier attempts to measure the size of the central object, just as fog blurs the glare of distant lighthouses.

“After 30 years, radio telescopes finally have lifted the fog and we can see what is going on,” said Heino Falcke, of the Westerbork Radio Observatory in the Netherlands, another member of the research team.

The bright, radio-emitting object would fit neatly just inside the path of the Earth’s orbit around the Sun, the astronomers said. The black hole itself, they calculate, is about 14 million miles across, and would fit easily inside the orbit of Mercury. Black holes are concentrations of matter so dense that not even light can escape their powerful gravity.

The new VLBA observations provided astronomers their best look yet at a black hole system. “We are much closer to seeing the effects of a black hole on its environment here than anywhere else,” Bower said.

The Milky Way’s central black hole, like its more-massive cousins in more-active galactic nuclei, is believed to be drawing in material from its surroundings, and in the process powering the emission of the radio waves. While the new VLBA observations have not provided a final answer on the nature of this process, they have helped rule out some theories, Bower said. Based on the latest work, he explained, the top remaining theories for the nature of the radio- emitting object are jets of subatomic particles, similar to those seen in radio galaxies and some theories involving matter being accelerated near the edge of the black hole.

As the astronomers studied Sagittarius A* at higher and higher radio frequencies , the apparent size of the object became smaller. This fact, too, Bower said, helped rule out some ideas of the object’s nature. The decrease in observed size with increasing frequency, or shorter wavelength , also gives the astronomers a tantalizing target.

“We think we can eventually observe at short enough wavelengths that we will see a cutoff when we reach the size of the black hole itself,” Bower said. In addition, he said, “in future observations, we hope to see a ‘shadow’ cast by a gravitational lensing effect of the very strong gravity of the black hole.”

In 2000, Falcke and his colleagues proposed such an observation on theoretical grounds, and it now seems feasible. “Imaging the shadow of the black hole’s event horizon is now within our reach, if we work hard enough in the coming years,” Falcke added.

Another conclusion the scientists reached is that “the total mass of the black hole is very concentrated,” according to Bower. The new VLBA observations provide, he said, the “most precise localization of the mass of a supermassive black hole ever.” The precision of these observations allows the scientists to say that a mass of at least 40,000 Suns has to reside in a space corresponding to the size of the Earth’s orbit. However, that figure represents only a lower limit on the mass. Most likely, the scientists believe, all the black hole’s mass — equal to four million Suns — is concentrated well inside the area engulfed by the radio-emitting object.

To make their measurement, the astronomers had to go to painstaking lengths to circumvent the scattering effect of the plasma “fog” between Sagittarius A* and Earth. “We had to push our technique really hard,” Bower said.

Bower likened the task to “trying to see your yellow rubber duckie through the frosted glass of the shower stall.” By making many observations, only keeping the highest-quality data, and mathematically removing the scattering effect of the plasma, the scientists succeeded in making the first-ever measurement of Sagittarius A*’s size.

In addition to Bower and Falcke, the research team includes Robin Herrnstein of Columbia University, Jun-Hui Zhao of the Harvard-Smithsonian Center for Astrophysics, Miller Goss of the National Radio Astronomy Observatory, and Donald Backer of the University of California-Berkeley. Falcke also is an adjunct professor at the University of Nijmegen and a visiting scientist at the Max-Planck Institute for Radioastronomy in Bonn, Germany.

Sagittarius A* was discovered in February of 1974 by Bruce Balick, now at the University of Washington, and Robert Brown, now director of the National Astronomy and Ionospheric Center at Cornell University. It has been shown conclusively to be the center of the Milky Way, around which the rest of the Galaxy rotates. In 1999, Mark Reid of the Harvard-Smithsonian Center for Astrophysics and his colleagues used VLBA observations of Sagittarius A* to detect the Earth’s motion in orbit around the Galaxy’s center and determined that our Solar System takes 226 million years to make one circuit around the Galaxy.

In March 2004, 55 astronomers gathered at the National Radio Astronomy Observatory facility in Green Bank, West Virginia, for a scientific conference celebrating the discovery of Sagittarius A* at Green Bank 30 years ago. At this conference, the scientists unveiled a commemorative plaque on one of the discovery telescopes.

The Very Long Baseline Array, part of the National Radio Astronomy Observatory, is a continent-wide radio-telescope system, with 10, 240-ton dish antennas ranging from Hawaii to the Caribbean. It provides the greatest resolving power , or ability to see fine detail, of any telescope in astronomy, on Earth or in space.

## A new view of the black-hole binary Cygnus X-1

It’s 5 AM, July 12th 2016, at the Esrange Space Centre in northern Sweden - the walkie-talkie crackles to life: “Operations to science - what is your status?” - the reply comes quickly “Science is go!”. Other stations are polled in turn and then we hear “Operations to launch officer - you have the balloon”. Shortly afterwards, the moment we had been waiting for - our two tonne X-ray telescope climbs into the atmosphere suspended under a fragile million cubic meter helium-filled balloon.

#### Share

. fast-forward to later that day and the balloon has reached 40 km altitude. The atmosphere is now sufficiently thin to allow us to observe the X-ray photons which started their journey 6000 light-years away at the black-hole binary Cygnus X-1. The data which appears in our paper was collected each day during the following week as the balloon is carried on the stratospheric winds from Sweden to Victoria Island, Northern Canada.

The PoGO+ balloon-flight in July 2016 - from launch to landing. Credit: SSC.

Comprising the first generally accepted black hole and a massive supergiant companion star, Cygnus X-1 is one of the brightest persistent sources of X-rays in the galaxy. The intense gravitational field of the black hole rips matter from the companion star onto a thin circulating accretion disk around the black hole. The disk is heated by friction and produces intense X-ray emission. Close to the black hole lies the corona - a hot, optically thin region where X-rays undergo Compton scattering on energetic electrons.

Current imaging instruments cannot resolve details of the binary system. The PoGO+ telescope has no imaging capability but, uniquely, it can determine the polarisation of incident X-rays, described by the polarisation fraction (%) and polarisation angle (degrees). X-rays become polarised when they scatter off the accretion disk with the details depending on the disk-corona geometry. The PoGO+ energy band is well matched to that of the flux reflected from the corona. PoGO+ discovered that only a small fraction of X-rays are polarised (<8.6% at 90% confidence level) and for these X-rays that the polarisation angle is aligned with the disk rotation axis. We interpret this as the X-ray emission not being influenced by the strong gravity of the black hole. This reveals that the accretion corona is an extended structure or lies far from the black hole - providing important new insights into black-hole binary accretion physics.

Arriving at this new view of Cygnus X-1 has been a long and, at times, frustrating journey - as experimental work often is. After spending a number of years working with telescope prototypes, and then building and calibrating the flight version, we turned our attention to balloon flights. Progress was not as straight-forward as we had hoped for. We experienced a failed balloon launch in 2011, a cancelled launch due to bad weather in 2012, and technical problems with the telescope in 2013 (moreover Cygnus X-1 was in an unfavourable spectral state, although we did manage to observe the Crab - but, that’s another story). We have certainly benefitted from the big advantage with stratospheric ballooning - that the telescope is returned to earth by parachute at the end of the flight, can be repaired/upgraded, and re-flown.

After a very successful balloon flight, resulting in the first polarimetric observations of both Cygnus X-1 and the Crab [Paper 1] [Paper 2] in hard X-rays, the PoGO+ project will now be retired. We are looking forwarding to taking on new challenges within the emerging field of X-ray polarimetry!

The PoGO+ campaign team. Left to right: J-E. Strömberg (DST Control), N. Uchida (Hiroshima University), C. Lockowandt (SSC), H-G. Florén (Stockholm Uni), M. Pearce (Principal Investigator, KTH), V. Mikhalev (KTH), H. Takahashi (Corresponding Author, Hiroshima Uni), M. Chauvin (KTH), M. Friis (KTH), T. Kawano (Hiroshima Uni), M. Kiss (KTH), T-A. Stana (KTH).

## Black Holes in Space Don’t Support Evolution!

Originally published in Creation 12, no 2 (March 1990): 29.

Black holes may or may not exist. If they do exist, they are invisible, weigh billions of tons, and are smaller than a kernel of corn!

While they have become popular with science-fiction buffs in recent years, black holes were first proposed some 200 years ago by French astronomer Pierre Laplace.

Laplace reasoned that a star must collapse when it dies, that is, when it consumes all its fuel. Because of its enormous gravitational pull, it would cave in on itself. It would shrink to the size of the moon, down to the size of a basketball, then finally it would effectively have no size at all.

When a star collapses below a certain radius, it would become so dense, and its gravitational pull so strong, that even light could not escape (hence the name “black hole”). Matter inside a black hole would be so dense that a piece less than one centimetre across could weigh as much as planet earth!

No black holes have yet been positively identified, and not all astronomers accept their existence. But even if black holes do exist, they give no support to the theory of evolution. Black holes are simply in line with the fact that the universe is decaying. Things do not spontaneously improve and become more orderly, as evolution theory would have people believe. They decay, run down, and lose their orderliness.

This is completely in line with creationist thinking. But it does not lend support to the evolutionary idea that today’s complexity has evolved and become more ordered from the chaos of long ago.

(Adapted from Astronomy and the Bible, Questions and Answers, by Donald B. DeYoung, Baker Book House, Grand Rapids, Michigan, 1989.)