Astronomy

If any object could become a black hole, could any object become a neutron star?

If any object could become a black hole, could any object become a neutron star?

A black hole doesn't necessarily need to form from a star; theoretically, it could form from any extremely dense object. In fact, many astronomers differentiate certain black holes, like supermassive ones, from stellar ones (ones that form from stars).

However, could the same apply for neutron stars? Neutron stars only form because of the intense gravity during a star's collapse: electron capture is forced to happen, and the majority of the star becomes neutrons. Could this potentially happen to non-stellar objects, if the gravity forces electron capture?

If so, why don't we see as many of these "neutron objects" as we do non-stellar black holes?


There can be no such thing as a "supermassive neutron star". The theoretical upper mass limit for a neutron star is somewhere between 2.2 and 3 solar masses. Any more massive and they inevitably form black holes. So I am not clear what kind of "neutron objects" you were thinking of?

Nor is it clear what you mean by "non-stellar" objects that will have the densities required to make neutron-degenerate matter? There aren't any apart from (I) the cores of massive stars at the ends of their lives. (II) Massive white dwarfs if they accrete matter over and above their Chandrasekhar limit. Furthermore, there is a minimum mass for a neutron star. Although the observed lower limit to those seen in nature is (so far) around $1.15 M_{odot}$, there is a theoretical lower limit of about $0.1$ to $0.2M_{odot}$ set by the stability of the neutron against decay in self-gravitating material ( See https://physics.stackexchange.com/questions/143166/what-is-the-theoretical-lower-mass-limit-for-a-gravitationally-stable-neutron-st/143174#143174 ).

It is true if you could arrange to compress any matter to densities above $sim 10^{15}$ kg/m$^3$ it would form neutron-degenerate material. But this requires (as far as we know) the conditions I listed above.


A neutron star will form if you have roughly 1.4-3 solar masses of matter which is not producing enough energy to hold itself up through radiation pressure. So in principle you could assemble 2 solar masses of iron and it would collapse under its own gravity and form a neutron star.

However, the vast majority of the universe is mixed hydrogen and helium, and if you assemble 2 solar masses of those materials, fusion will start well before it collapses and you get a normal star. So it seems likely that every natural neutron star in the real universe will have been through a nuclear burning phase, and so be a "stellar" neutron star.

It is just conceivable that a density fluctation in the very early universe might have been just the right size that the matter there cooled to neutronium rather than just a denser cloud of normal matter, but it would have been surrounded by fairly dense normal matter, so would probably grow into a black hole.


As others have pointed out, the reason why we don't see non-stellar neutron stars is that the pressures needed to form them are usually only found in stars. Lower pressures don't form neutron degenerate matter and higher pressures form black holes.

I think part of your question may be whether or not smaller quantities of neutron-degenerate matter, which would be under lower constant pressure, are stable. I think the answer is either "no" or "not very much lower pressure", since even the crusts of neutron stars are believed to have separate nuclei: https://link.springer.com/article/10.12942/lrr-2008-10 . In small quantities, neutron-degenerate-matter would probably explode with extreme force, as if were just a ridiculously superheavy and super-neutron-rich atom: https://physics.stackexchange.com/questions/10052/what-would-happen-to-a-teaspoon-of-neutron-star-material-if-released-on-earth

However, some theories suggest that this would not be true for denser types of quark-gluon matter that are likely to be found inside massive "neutron stars". The concept of "strange matter" made of up, down, and strange quarks is well known, and it is has been famously predicted by some to be stable at room temperature, after it has been formed, perhaps even converting normal matter it touches into strange matter (or, alternatively, maybe not). "Strangelets", or tiny pieces of strange matter, are one candidate for what dark matter could be, and it has even been suggested that they might hit Earth about once a year and explain some weird craters: https://arxiv.org/ftp/arxiv/papers/2007/2007.04826.pdf

Similarly, it has also been suggested that very heavy atomic nuclei (A>about 300), may collapse into a sea of up and down quarks called "up-down quark matter" or udQM, which might actually be more stable than "strange matter" (uds-matter). This has been suggested to create a "continent of stability", where nuclei this big are actually stable, unlike smaller superheavy nuclei, and has been suggested as an alternative to strangelets as a dark matter candidate: https://en.wikipedia.org/wiki/Continent_of_stability

Needless to say, both of the types of QCD-matter are extremely theoretical because A) only supernova-like pressures can create them, even if they do turn out to be stable or metastable at low pressure, B) our methods of making superheavy nuclei with particle accelerators have not progressed that far yet, C) the proper quantum-chromodynamics calculations are very difficult to do, and really good calculations of this sort have only been done for small nuclei, so the math these predictions (including the one about neutron-degenerate matter) are based on is all approximations that probably introduce significant errors.

It is possible that further investigations of neutron-star collisions will reveal more about the nature of their interiors, and whether these collisions might even be able to liberate some ultradense matter without it decaying into normal-sized nuclei. (If it doesn't, that doesn't mean this ultradense matter couldn't be stable, since it could just be the energy of the collision that destroyed it, and even if it does, such a source is not likely to be a major source of dark matter, because that would result in the amount of dark matter increasing as the universe aged, which I think goes against observation.)


At what point would the Earth become a black hole?

Pretty much anything could, in theory, become a black hole if it were squeezed down small enough. At what point would the Earth become a (very unimpressive) black hole in space? We're going to figure it out, and tell the tale of the Schwarzschild Radius.

Karl Schwarzschild is one of those people who make us resentfully conscious of just how little we get done during our days. He was a well-respected professor of astrophysics in Germany, one of the major centers of physics research. When World War I broke out, he enlisted in the army, and was sent to the Russian front. There wasn't really a pleasant front in World War I, but Russia was extra-tough, and everyone would have understood if he had just concentrated on staying alive. Instead, he got some reading material, which happened to be Einstein's Theory of General Relativity. This theory has Einstein stating that massive objects distort spacetime, and that distortion is what we perceive as gravity. Schwarzschild considered this, and thought that a massive enough object packed into a small enough space could distort spacetime enough that not even light could escape it. As there was nothing currently on his plate (probably literally), he decided to go ahead and work out that relation of mass and the space it was packed into.

He came up with the idea that the radius within which an object became a black hole could be calculated by doubling the object's mass, multiplying it by the universal gravitational constant, and dividing the entire thing by the speed of light squared. In other words:

This technically means that anything can become a black hole, as long as it's compressed down enough. "Technically" isn't the same as "practically." Recently scientists were surprised that a star forty times as massive as the sun failed to produce a black hole after its collapse. But, if we had some preternatural mass-hugger out there, almost anything could be compressed into black hole if it got pushed within its own Schwarzschild Radius. It would have to be a hell of a hug — to get the sun to turn into a black hole, it would need to be pushed down to about three kilometers in radius. The Earth would need to be pressed into having a radius of 8.7 millimeters. One could think of that as very unimpressive, but I like to think of it as being like a tiny space assassin.

Sadly, Schwarzschild died of infection within a year of coming up with his eponymous calculation. He never got to see black holes, or wide acceptance of his idea. But he certainly got a lot done.


Black hole shatters physics after devouring unknown object 'Haven't seen anything like it'

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Black hole: Animation outlines how the 'heartbeat' works

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Black holes are regions of spacetime that form when massive stars collapse at the end of their life cycles and can continue to grow by absorbing stars and merging with other black holes. This interaction allows scientists to identify their presence, as electromagnetic radiation is given off as visible light across space. In this way, astronomers have identified numerous stellar black hole candidates in binary systems and established that the radio source known as Sagittarius A*, at the core of the Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses.

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But 800 million light years away, a black hole devoured an unidentified object and the resulting cosmic merger released enough energy to wrinkle the fabric of spacetime.

These gravitational waves travelled through the universe and eventually over Earth on August 14, 2019.

Three detectors in the US sensitive enough to measure such minuscule action recorded the activity, but as scientists decoded the information they were left scratching their heads.

Vicky Kalogera of Northwestern University, who coordinated the report on the merger, said: &ldquoWe haven&rsquot seen, with confidence, anything like this before.&rdquo

The black hole devoured an unknown object (Image: GETTY)

Blackholes are regions of spacetime (Image: GETTY)

Published in Astrophysical Journal Letters in June, researchers said the collision, called GW190814, stands out from the dozens of cosmic mergers detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO).

For millions or perhaps billions of years, the two objects orbited one another, spiralling closer and closer until they finally collided.

Astronomers determined that one of those objects was a black hole with as much mass as 23 Suns and the other mystery object was roughly 2.6 solar masses.

The unknown phenomenon has baffled scientists because its mass places it somewhere between being the heaviest known neutron star, or the lightest black hole.

Dr Kalogera added: &ldquoIf it&rsquos a neutron star, it&rsquos an exciting mass for a neutron star. If it&rsquos a black hole, it&rsquos an exciting mass for a black hole.

The activity was picked up by LIGO (Image: GETTY)

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&ldquoEither way, it perked up our antennae the moment we saw it.&rdquo

Observations suggest the heaviest neutron star is around 2.1 solar masses, but most are close to around 1.4, while the lightest black holes are about five solar masses.

The University of Arizona&rsquos Feryal Ozel, who studies the boundaries on these objects said: &ldquoIf it ends up being a neutron star &ndash if a neutron star can be as massive as 2.6 solar masses &ndash it is truly paradigm-changing.&rdquo

The two scientists both suspect the mystery object is a black hole, but note it will be difficult to prove either way.

Scientists were left baffled (Image: WIKI)

Now astronomers must work to find out more (Image: GETTY)

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Dr Ozel added: &ldquoI don&rsquot think we have any chance of knowing what this object is.

&ldquoThe telltale signs that it could have been a neutron star are simply not there &ndash but their absence doesn&rsquot mean anything, either.&rdquo

Even without knowing what the object is, the event is unique because they are so mismatched, shattering what astronomers thought they knew about how the cosmic phenomena behave.

Most collisions involve pairs that are relatively similar in mass, but at 23 solar masses, this black hole is roughly nine times heavier than its lighter partner.


Can an object become a black hole by moving fast enough?

this week in school we have been learning about special relativity and we learnt that an objects mass increases as its speed approaches c. Does this mean there would be a point where its mass is large enough that it could become a black hole?

Here is my (well-deserved) rant against relativistic mass. (Your answer is buried in there somewhere. The answer is "no".)

I honestly do not know why many intro texts, courses, and teachers insist on telling students that an object's mass increases as its speed increases. This concept is so incredibly misleading and incorrect, that it's no wonder so many students are confused by it.

The concept of relativistic mass is used only in some vain attempt to keep the Newtonian formula for momentum (p = mv) true in relativity as well. That seems like a good idea, for then the formula for total energy would be rather simple also (E = mc 2 ). Beyond those two very specific uses, there is no use for the concept of relativistic mass and you just end up getting a bunch of nonsense.

For one, you find that Newton's second law no longer has the nice formula F = ma, and you have to assign different relativistic masses to each direction of the force. That is, in SR, the force is not always parallel to the acceleration, and the "mass" appearing in the tangential direction is different from the "mass" appearing in the transverse direction. Second, we end up getting rather nonsensical implications, like that which the OP has come across. If mass increases as an object's speed increases, then eventually it should be massive enough to be within its own Schwarzschild radius and become a black hole. but in its own rest frame it's not massive enough. So what's going on? (It's not a black hole.)

Relativistic mass is really just another name for the energy E. So where does relativistic mass come from anyway? The formula for the momentum of a particle with "rest mass" m and velocity v in SR is p = γmv, where γ is the Lorentz factor. So to retain the formula p = Mv, we define a new "relativistic mass" given by M = γm. But it's actually just much more natural to define a new quantity called the 4-velocity, whose spatial components are γv. The time-component is γc, and the whole thing is U = (γc, γv). The 4-momentum is then P = mU, in analogy with Newtonian physics. The mass of a particle is then invariant. All observers agree on the value of m.

Relativistic mass is really just a desperate attempt to hang on to old formulas and concepts from Newtonian physics. An object that is accelerated does appear to have increasing inertia, but only if you look at the problem from a Newtonian view. The object's speed cannot exceed c. If the object (in its own frame) is accelerating at some constant (proper) acceleration a, the outside observer will see the object slowly decelerate to zero acceleration as its speed approaches c. So it appears as if the inertia (the m appearing in F = ma) is increasing. This is a terrible way to analyze that problem. For one, this analysis is based on Newton's second law, yet the relativistic mass is related to the number m appearing in the momentum formula p = mv. This is a subtle issue. In Newtonian physics, the "m" appearing in F = ma and p = mv are automatically the same number. But if you carry out the above analysis that the accelerating object's inertia is increasing, then you have to give up the notion that the "inertial mass" and "momentum mass" are actually the same. (Again, the reason is that the force is actually not parallel to the acceleration in general, and to have any hope of consistency, relativistic mass would have to be different in the transverse and parallel directions.) Today, we understand that energy plays that inertial role. The mass doesn't change, but the energy formula has changed in such a way that the object's energy approaches infinity as its speed approaches c.

Why jump though all those hoops and redefine the concept of mass in such a way that turns out to be woefully inconsistent once you start to analyze more complex problems? It's better just to realize that relativity requires that the universe has a different geometry than that of Newtonian physics. The impossibility of an object's speed exceeding c has nothing to do with increased inertia, but rather the underlying geometry of the universe. Thus it is more natural to change how we view and define position and velocity, especially once we see that time and space must be unified into spacetime. (Of course, once you go to GR, despite the difficulties in defining mass, it is very immediately obvious that you should not define it in a frame-dependent way. So relativistic mass is super incorrect in GR.)

Despite Einstein himself discouraging the use of relativistic mass, the concept became very popular. In the late 1980s, several physicists began a bit of a movement against relativistic mass. I was in high school in the early 2000s when I first learned physics, and I have never personally used a text or taken a course that used relativistic mass. (I didn't even realize such a concept existed until halfway through college when I came across an old text on relativity.) So I am guessing that somewhere in the 1990's or maybe even the early 2000s, the majority of physicists had gotten on board with the death to relativistic mass. So today when I read questions like that of the OP, I just cringe and wince. Who the hell is out there still teaching this terrible and outdated concept? Ugh.


New Kind of Space Explosion Reveals the Birth of a Black Hole

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Photograph: SAKKMESTERKE/Science Source

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In 2018, astronomers were shocked to find a bizarre explosion in a galaxy 200 million light-years away. It wasn’t like any normal supernova seen before—it was both briefer and brighter. The event was given an official designation, AT2018cow, but it soon went by a more jovial nickname: the Cow.

Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation whose mission is to enhance public understanding of science by covering research develop­ments and trends in mathe­matics and the physical and life sciences.

The short-lived event—known as a transient—defied explanation. Some thought it might be a star being torn apart by a nearby black hole, but others favored a “failed supernova” scenario, where a black hole quite literally eats a star from the inside out. To find out for sure, they needed to find more Cow-like events.

More than two years later, they got one.

Beginning on October 12, 2020, telescopes watched as something in a galaxy 3 billion light-years away became incredibly bright, then disappeared from view. It behaved almost identically to the Cow, astronomers reported in a paper posted to the online preprint site arXiv.org last week, leading them to conclude that it must be the same type of episode. In keeping with tradition, it was given its own animal-inspired name: the Camel.

“It’s really exciting,” said Deanne Coppejans, an astrophysicist at Northwestern University. “The discovery of a new transient like AT2018cow shows that it’s not a complete oddball. This is a new type of transient that we’re looking at.”

The Cow was a complete surprise, and astronomers weren’t really sure what they were looking at when it appeared. The Camel, in contrast, was like a burglar tripping the new alarm system. “We were able to realize what it was within a few days of it going off,” said Daniel Perley, an astrophysicist at Liverpool John Moores University who led the new study. “And we got lots of follow-up data.”

Four days later, the team used telescopes in the Canary Islands and Hawaii to obtain vital data on its properties. They later put out an alert to other astronomers on a service called the Astronomer’s Telegram.

The event was given two designations. One, AT2020xnd, came from a global catalog of all transients, and the other, ZTF20acigmel, came from the Zwicky Transient Facility, the telescope where it was discovered. The team twisted the latter into its “Camel” nickname. “Xnd didn’t quite have the same ring to it,” said Perley.

Like its predecessor, the Camel became very bright in a short time, reaching its peak in two or three days. It grew about 100 times brighter than any normal type of supernova. Then it rapidly dimmed in a process that lasted just days, rather than weeks. “It fades very fast, and while it’s fading it stays hot,” Perley said.

Prior to this discovery, astronomers had sifted through historical data to find two additional Cow-like events, the “Koala” and CSS161010, but the Camel is the first to be seen in real time and thus studied in detail since the Cow.

The four events have similar properties. They quickly get bright, then fade fast. They’re also hot, which makes them look blue. But these “fast blue optical transients” are not identical.

“The explosion itself and the sort of zombie afterlife behavior, those are quite similar,” said Anna Ho, an astrophysicist at the University of California, Berkeley, who discovered the Koala and was part of the Camel discovery team. The events all appear to be some sort of explosion from a star that collides with nearby gas and dust. “But the collision stage where you’re seeing the explosion collide with ambient material, that has shown some variation in the amount of material lying around and the speed in which the shock wave from the explosion is plowing through the material.”

The leading idea at the moment is the failed-supernova hypothesis. The process begins when a massive star around 20 times the mass of our sun reaches the end of its life and exhausts its fuel. Its core then collapses, beginning what would normally be a regular supernova, where infalling material rebounds back out, leaving behind a dense object called a neutron star.

But in cases like the Camel and the Cow, “something unusual happens in the process to core collapse,” said Perley. “What we claim is that instead of collapsing to a neutron star, it collapsed straight into a black hole, and most of the star fell into the black hole.”


Gravitational wave mystery could be a sign of a new kind of black hole

A strange set of gravitational waves have been sent across space by a mysterious object. It could be the smallest black hole ever found or the largest neutron star.

Gravitational waves are ripples in space-time that are caused by the motion of massive objects. The Laser Interferometer Gravitational-Wave Observatory (LIGO) has detected these waves from many pairs of black holes colliding over the past few years, as well as one pair of neutron stars.

Now they have found a truly puzzling collision, LIGO team member Katerina Chatziioannou told a meeting of the American Astronomical Society in Hawaii on 6 January. A LIGO detector in Louisiana spotted signs of two objects colliding, but nobody is quite sure what one of the objects is.

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In this smash-up, one of the objects was definitely a neutron star with a mass between 1.1 and 1.7 times the mass of the sun. While the other object is probably also a neutron star, months of analysis haven’t been able to prove this, says LIGO team member Nelson Christensen.

Its mass could be as high as 2.5 times that of the sun, which means it could be massive enough to be a black hole.

Read more: Black hole that ‘rings’ like a bell shows Einstein was right

“We’ve never seen any neutron star with this large a mass,” says Christensen. “The question is, is it really a neutron star? If it is, then we’ve detected a really strange heavy neutron star, but if it’s a black hole it’s a really light black hole.”

While the idea of such a low-mass black hole is plausible, the lightest one anyone has found thus far is 3.3 times the mass of the sun. If it isn’t the smallest black hole ever found, but in fact a neutron star, this object is still unusual because it isn’t clear how a neutron star with a nearby partner could get so large.

“It’s clearly heavier than any other pair of neutron stars ever observed,” said Chatziioannou in a press conference. “The existence of a system like that challenges our current understanding of how those systems form binaries and merge to give off gravitational waves.”

We should get used to this kind of strange discovery, says Christensen. “We’re getting about one gravitational wave event a week now, and that’s a lot,” he says. “With a lot of events you inevitably see cool stuff every now and then.”


Black Holes have no Hair

This may seem like an odd title, and it is, but trust me when I say that it is a perfectly acceptable phrase in physics. It refers to the fact that all you need to perfectly describe any black hole is 3 externally observable numbers, the rest of the information (hair) about the matter that made the black hole is lost. The 3 numbers you need to describe a black hole are its Mass (), Angular Momentum () and Charge (). All other information is lost, which is potentially a huge amount, as a black hole with a given , and can be formed from many different collections of particles.

So if you had two stars with the same values for , , and , but one was made of matter and the other antimatter, then when they collapsed to black holes they would be identical. You wouldn’t be able to tell which was which. Information is lost behind the event horizon.

The main equations we have so far for a black hole are 3, 4 and 5. As you can see, the only variable in equations 3 and 4 is mass (). Equation 5 only depends on the surface are of the event horizon , however the surface area of a sphere depends on its radius, and from equation 3 we know that radius depends on .


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The announcement is the latest in a line of spectacular discoveries whereby gravitational waves – tiny ripples that spread through space and time when two massive objects collide – have been detected on Earth.

They are used to paint a picture of some of the biggest, most violent and unusual cosmic events happening across the Universe.

'When I first saw the alert come through, my jaw hit the floor,' said Charlie Hoy from Cardiff University, who worked with LIGO when the discovery was made.

'It was not until I saw the significance of this event that it hit me how important this event could be for astrophysicists around the world,' he said.

'This was the first possible detection of a highly significant neutron star-black hole candidate - something that we had previously never seen before.'

Cardiff University has been involved in the US-backed LIGO since its inception and the university's Gravity Exploration Institute has developed algorithms and software that have become standard tools for detecting gravitational wave signals.

The latest detection of gravitational waves, using sophisticated detectors in the US and Italy, actually took place on August 14, 2019.

This graphic shows the masses of black holes detected through electromagnetic observations (purple), black holes measured by gravitational-wave observations (blue), neutron stars measured with electromagnetic observations (yellow), and neutron stars detected through gravitational waves (orange)

Since then, Hoy and colleagues has been leading the 'parameter estimation' for this particular event on behalf of LIGO.

This involved untangling the gravitational wave signals and matching them with millions of possible combinations to determine the properties of the objects that produced the gravitational waves in the first place.

This includes parameters such as their mass, the speed and direction at which they were spinning and their distance from Earth.

'Being a junior member of the collaboration responsible for a significant chunk of the analysis and the writing of the discovery paper has been a huge learning experience, and one that I am hugely grateful for being part of,' said Hoy.

The gravitational waves emitted from this particular event, which has been dubbed GW190814, led to the creation of a black hole 25 times the mass of the Sun.

The mysterious object is believed to have had a mass 2.6 times that of the sun, placing it firmly in the so-called 'mass gap'.

The collision of the two objects generated gravitational waves that spread across the universe and hit the Earth

The two objects - one of which was a black hole 23 times the mass of the Sun - merged to form a larger black hole 25 times the mass of the Sun

'Whether any objects exist in the mass gap has been an ongoing mystery in astrophysics for decades,' Hoy continued.

'What we still don't know is whether this object is the heaviest known neutron star or the lightest known black hole, but we do know that either way it breaks a record.

'What is really exciting is that this is just the start. As the detectors get more and more sensitive, we will observe even more of these signals, and we will be able to pinpoint the populations of neutron stars and black holes in the universe.'

Dr Vivien Raymond, a member of the LIGO team based at Cardiff University's School of Physics and Astronomy, said this new detection pushes boundaries of what we know about neutron stars and black holes.

'This new event in particular involved joint efforts by many different international experts in the collaboration, and we are trying to get ready for the next surprise nature will reveal,' said Raymond.

Professor Sheila Rowan, Director of the University of Glasgow's Institute for Gravitational Research (IGR), said the discovery was nearly missed altogether.

'It's possible that that we might have missed it altogether if we hadn't taken that time to reflect on and learn from our early successes,' said Rowan.

More cosmic observations and research will need to be undertaken, to establish whether this new object is indeed something that has never been observed before or whether it may instead be the lightest black hole ever detected.

It could also be the heaviest neutron star ever detected, researchers say.

The new findings from the LIGO Scientific Collaboration and the European Virgo Collaboration have been published in The Astrophysical Journal.

WHAT ARE GRAVITATIONAL WAVES?

Scientists view the the universe as being made up of a 'fabric of space-time'.

This corresponds to Einstein's General Theory of Relativity, published in 1916.

Objects in the universe bend this fabric, and more massive objects bend it more.

Gravitational waves are considered ripples in this fabric.

Gravitational waves are considered ripples in the fabric of spacetime. They can be produced, for instance, when black holes orbit each other or by the merging of galaxies

They can be produced, for instance, when black holes orbit each other or by the merging of galaxies.

Gravitational waves are also thought to have been produced during the Big Bang.

Scientists first detected the shudders in space-time in 2016 and the discovery was hailed the 'biggest scientific breakthrough of the century'.

Experts say gravitational waves open a 'new door' for observing the universe and gaining knowledge about enigmatic objects like black holes and neutron stars.


Is it a neutron star or black hole? Astronomers are confused by this mysterious object

On August 14, 2019, astronomers discovered evidence of something mysterious they're only starting to understand.

It started with gravitational waves, which were detected by observatories in Washington and Italy. The signal of those waves a result of two massive cosmic objects crashing and then merging into one another — a black hole that's about 23 times as massive as the Sun and a second mysterious object of 2.6 solar masses.

The object in question remains unclassified as it falls within an elusive mass gap which makes it either the lightest known black hole or the heaviest known neutron star.

The detection of the mysterious object is detailed in a study published this week in The Astrophysical Journal Letters.

The death of stars can result in two objects black holes or neutron stars. As a star nears the end of its life, it runs out of fuel and collapses under the weight of its own gravity. The larger stars leave behind a black hole, a great amount of matter packed into a tight area of space, while the remnants of slightly smaller stars create neutron stars, an extremely dense, dead core of a star.

The lightest black hole is about five times the mass of the Sun, while the heaviest neutron stars are 2.5 times the mass of the Sun.

However, this newly discovered object is 2.6 times the mass of the Sun, which makes it neither a light black hole nor a heavy neutron star. Instead, it exists in the yet undefined 'mass gap' between the two objects.

"Even though we can't classify the object with conviction, we have seen either the heaviest known neutron star or the lightest known black hole," Vicky Kalogera, a professor of physics and astronomy at Northwestern's Weinberg College of Arts and Sciences, who coordinated the writing of the new paper, said in a statement. "Either way, it breaks a record."

This so-called mass gap has intrigued astronomers for decades, but this discovery marks the first time an object fits right into the gap between black holes and neutron stars.

The merger of this mysterious object with the larger black hole was detected by the National Science Foundation's Laser Interferometer Gravitational-Wave Observatory (LIGO) and the European Virgo observatory, and dubbed GW190814.

The merger resulted in a black hole that's about 25 times the mass of the Sun, located around 800 million light-years away from Earth.

Before they merged, the masses of the two objects differed by a factor of nine which made this merging event the most extreme mass ratio of any gravitational wave event detected.

"I think of Pac-Man eating a little dot," Kalogera said. "When the masses are highly asymmetric, the smaller compact object can be eaten by the black hole in one bite."

However, the researchers behind the new study believe that this type of merger could occur a lot more frequently than previous models have predicted.

Although astronomers are not able to define this freak of nature just yet, they are hoping that future observations of similar merger events or of objects that fit into this odd mass gap will help them identify whether the mysterious object is a black hole or neutron star.

"This observation is yet another example of the transformative potential of the field of gravitational-wave astronomy, which brings novel insights to light with every new detection," Pedro Marronetti, program director for gravitational physics at the National Science Foundation, said in a statement. "[It] cannot be explained without defying our understanding of extremely dense matter or what we know about the evolution of stars."


6 Answers 6

The question really boils down to the dynamics of event horizons when black holes merge. It turns out that there are some great simulations that explore these dynamics. If one scrolls down to the bottom of this black-holes.org page one can see a video of the merging of two different sized black holes. One can review the underlying paper and see that the actual development of the simulation was very extensive.

The actual event horizons do move and oscillate, so the question is whether the spaceship itself has become some sort of physical element of the black hole after it has crossed the event horizon. Since it is argued in most cases that space craft can cross the event horizon in large black holes without witnessing any sort of significant effect, although the spacecraft's mass must be considered part of the black hole's mass after crossing the event horizon, it still has some freedom of movement.

We can see from the simulation that the geodesics that define the event horizon fluctuate when the holes merge. So if the geodesics fluctuate is it possible that the spacecraft would find itself on a geodesic that suddenly allows for an escape?

The answer should be no. The geodesics defining the horizon require trajectories with velocities greater than the speed of light. The spacecraft can not exceed the speed of light. So while the geodesic its on might distort during the merger of the black hole, it is the underlying space itself that is distorting, which is not going to impart some ability to defy local laws of physics to the space craft. As such, it will stay inside the blackhole horizon since its geodesic, while distorted, will still remain inside the horizon.