I did some googling around and couldn't get answer to a simple question of black hole mass compared to the star from which it was created. It is well known that giant stars burn very bright and relatively very quickly. They end up their lives as red giants and eventually collapse into a black hole.
Suppose that the star is mid-life and has some mass M. Over the time it burns its fuel, turns into a red giant and after supernova, turns into a black hole. This black hole has some mass B. Why B >> M?
According to some simple physics laws, mass could not be created nor destroyed.
The mass of a black hole is always much less than the star from which it formed.
A very large star such as Eta Carinae (which is expected to form a black-hole some day) is about 100 times that of the sun, Having already lost as much as 50 solar masses, blown off the star by powerful outbursts in the past.
The future of the star is not fully understood. It is possible that it will collapse in a supernova, in which most of the rest of the star will be blasted into space, forming a supernova remnant, and the core of the star will collapse. The black hole formed may have a mass of more than 3 times the sun, but much less than the mass of the original star.
So while the black hole is not heavier, it is much denser. A 3 solar mass black hole would have a diameter of about 20km.
LIGO and Virgo detected a collision between a black hole and a mystery object
In a first, the LIGO and Virgo gravitational wave detectors have spotted a collision between a black hole (illustrated left) and a mystery object (right), which could be either the heaviest neutron star ever discovered or the lightest black hole.
R. Hurt/MIT/Caltech/LIGO (IPAC)
Ripples in spacetime have revealed a distant collision between a black hole and a mystery object, which appears too massive to be a neutron star but not massive enough to be a black hole.
At first glance, the event — detected by the LIGO and Virgo gravitational wave detectors on August 14, 2019 — looked like a collision between a black hole and neutron star (SN: 8/15/19). But a new analysis of the gravitational waves emanating from the merger tells a different story. It shows that a black hole about 23 times as massive as the sun crashed into a compact object of about 2.6 solar masses, researchers report June 23 in the Astrophysical Journal Letters.
That 2.6-solar-mass object is heavier than the presumed 2.5-solar-mass cap on neutron star size. But it’s smaller than the most lightweight black hole ever observed, which is about five solar masses. “We have [here] either the heaviest known neutron star … or we have the lightest known black hole,” says Cole Miller, an astrophysicist at the University of Maryland in College Park not involved in the work.
Neutron stars, which are dense stellar remnants left behind by stellar explosions, are thought to max out at about 2.5 solar masses because any larger star is liable to crumple under its own weight. Black holes less than about five solar masses are theoretically possible, “we just have had no observational evidence of such low-mass black holes,” says coauthor Vicky Kalogera, an astrophysicist at Northwestern University in Evanston, Ill. That could mean such objects are very rare, or that they’re just so difficult to spot that they’ve been overlooked in past searches.
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Unfortunately, this lone merger did not leave behind enough clues for astronomers to figure out the identity of the enigmatic 2.6-solar-mass object. After the U.S.-based Advanced Laser Interferometer Gravitational-Wave Observatory, or LIGO, and its sister experiment in Italy, Advanced Virgo, detected the merger, dozens of ground-based and space telescopes scoured the sky for light radiating from the crash site. But they found nothing.
That observation — or lack thereof — fits with the idea that the mystery object is a black hole, because black hole collisions are generally not thought to give off any light. But it could also fit with the neutron star explanation. Although smashups involving neutron stars can throw off a lot of light (SN:10/16/17), it’s possible that this collision — nearly 800 million light-years away —was simply too far away for telescopes to see its radiation. Or perhaps the black hole swallowed its little neutron star companion in a single gulp, causing it to vanish without a trace.
If that last scenario is true, “this means that [the pair of objects] had its moment of gravitational wave glory,” Miller says, and now the larger black hole forged in the merger is “doomed to wander the vast emptiness of space, probably never emitting another peep.”
Observations of similar events in the future might offer evidence in favor of either the small black hole or big neutron star theory, Kalogera says. If midsize objects in future collisions all tend to be between about 2.5 and three solar masses, she suspects that would mean astronomers are uncovering a heavier variety of neutron star that has been seen in the past. If, on the other hand, astronomers detect many objects whose masses run the gamut from about 2.5 to five solar masses, that may point to filling in a population of previously overlooked, petite black holes.
Kalogera and Miller both lean more toward the idea that the mystery object is a lightweight black hole than a heavyweight neutron star. If it is, that raises another question: how such a pint-size black hole got paired up with a partner so much bigger than itself.
Black holes usually team up with partners of similar heft. Most mergers detected by LIGO and Virgo have involved fairly equally matched black holes (SN: 4/20/20). But the larger black hole implicated in this merger was about nine times as massive as its enigmatic counterpart, raising questions about what could have brought such a strange couple together. Here, too, astronomers hope future gravitational wave observations of such oddball pairings may offer answers.
Questions or comments on this article? E-mail us at [email protected]
A version of this article appears in the August 1, 2020 issue of Science News.
Scientists thought all black holes emerged from exploding or collapsed stars. New evidence throws a wrench in that
Astrophysicists have found indirect evidence regarding the formation of black holes that, if confirmed, could upend our understanding of these stellar phenomena.
A paper published in Astrophysical Journal Letters by researchers Shantanu Basu and Arpan Das of University of Western Ontario provides evidence that it is possible for supermassive black holes to form without a very big star imploding. Rather, the study says that some supermassive black holes grow very fast over a very short amount of time, and then suddenly stop growing. The new model provides scientists with an explanation on how black holes formed during the very early stages of our universe.
"This is indirect observational evidence that black holes originate from direct-collapses and not from stellar remnants," Basu, an astronomy professor at the University of Western Ontario, said in a news release.
Most black holes that we know of are created in the heart of very large stars, many masses larger than our sun. Stars, by definition, fuse smaller atomic nuclei into heavier ones, in processes that create successively larger and heavier nuclei within the star. In a sufficiently massive star with a very dense core, the gravitational force will eventually overcome the other repellant forces that keep the nuclei apart, which will result in a spontaneous collapse into a single point whose escape velocity is greater than the speed of light — by definition, a black hole.
Such collapses are usually paired with an accompanying massive explosion of said star's outer shell of gas and dust. These explosions create stellar nebulae from which new stars and solar systems form (including our own).
But the existence of supermassive black holes, those beyond ten or twenty times our sun's mass, posed a problem for astronomers. How did they form, if not from a single collapsing star? The "direct-collapse" scenario, which Basu and Das provide evidence for, suggests that it is possible for a large quantity of interstellar gas and dust (not a star) to be spontaneously shoved down into an incredibly massive black hole — one far larger than those created by individual stars going supernova.
Astronomer Ethan Siegel explained the theoretical process of direct collapse in a Forbes article previously:
“Supermassive black holes only had a short time period where they were able to grow fast and then at some point, because of all the radiation in the universe created by other black holes and stars, then their production came to a halt,” Basu said. “That’s the direct-collapse scenario.”
These early-universe black holes have challenged our understanding of their formation and growth in the universe. In March, astronomers announced they had discovered 83 new supermassive black holes in the early universe, representing a time when the universe was less than 2 billion years old.
It has been a big year for black hole research. On April 10, the Event Horizon Telescope Collaboration (EHT) presented the first-ever direct image of a black hole. The blurry composite embodied over two centuries of advances in mathematics, science and electronics. Prior to the image, only artistic illustrations were available to depict the mysterious singularities that warp the spacetime continuum by virtue of their huge masses, producing such gravitational force that not even light can escape.
How do you weigh a black hole?
As Earth moves around the Sun, we see Cygnus X-1 from different vantage points. It appears to move back and forth very slightly against stationary background objects, in an effect we call “parallax”.
The amount of this tiny motion lets us calculate the distance between us and Cygnus X-1. But for an accurate measurement, we also had to take into account the orbital motion of the black hole around its companion star.
With a network of radio telescopes, we mapped out the black hole’s orbit, with a positional accuracy the equivalent of localising an object on the Moon to within ten centimetres.
By using our distance to Cygnus X-1 and the brightness and temperature of the star, we computed the size of the star. With this knowledge and the measured motion of the star during its orbit around the black hole, we could determine the black hole’s mass.
It is almost 50% more massive than previously thought, with a mass that’s 21 times that of the Sun.
Selected star - show another
VY Canis Majoris (VY CMa) is a red hypergiant star located in the constellation Canis Major. One of the largest stars and also one of the most luminous of its type, it has a radius of approximately 1,420 ± 120 solar radii (equal to a diameter of 13.2 astronomical units, or about 1,976,640,000 km), and is situated about 1.2 kiloparsecs (3,900 light-years) from Earth. VY CMa is a single star categorized as a semiregular variable and has an estimated period of 2,000 days. It has an average density of 5 to 10 mg/m 3 . If placed at the center of the Solar System, VY Canis Majoris's surface would extend beyond the orbit of Jupiter, although there is still considerable variation in estimates of the radius, with some making it larger than the orbit of Saturn.
The first known record of VY Canis Majoris is in the star catalogue of Jérôme Lalande, on March 7, 1801. The catalogue listed VY CMa as a 7th magnitude star. Further studies on its apparent magnitude during the 19th century showed that the star has been fading since 1850.
Since 1847, VY CMa has been known to be a red star. During the 19th century, observers measured at least six discrete components to VY CMa, suggesting the possibility that it is a multiple star. These discrete components are now known to be bright areas in the surrounding nebula. Visual observations in 1957 and high-resolution imaging in 1998 showed that VY CMa does not have a companion star.
Was biggest black-hole merger more lopsided than previously thought?
A compelling alternative explanation for what astrophysicists believe is the largest black hole merger measured to date has been put forth by two astronomers in Germany. Alexander Nitz and Collin Capano at the Max Planck Institute for Gravitational Physics argue that the gravitational wave GW190521 created by the merger could have been triggered by a stellar-mass black hole spiralling into a far larger body. If correct, their results could resolve a mystery surrounding the masses of both bodies in the merger and may lead to a better understanding of intermediate-mass black holes.
In May 2019, the LIGO and Virgo observatories detected gravitational waves originating from a black hole merger that created a new body weighing in at about 140 solar masses – making this the largest black hole merger seen so far. Subsequent calculations showed that the two black holes responsible for the GW190521 signal measured roughly 85 and 66 solar masses. Yet these values seem to be at odds with our current understanding of stellar evolution.
When giant stars of about 65–120 solar masses explode as supernovae, current theories predict that the explosions completely overwhelm the gravity holding the star together. As a result, no material is left behind after the explosion – not even a black hole. This should create a gap in the mass range of black holes formed from exploding stars, however both objects involved in the GW190521 merger appear to fall inside this gap.
To extract information about black hole masses from gravitational waves, astronomers must compare their observations to theoretical models, which incorporate prior assumptions about the physics. By selecting different priors and constraints, researchers can fine-tune their models to better fit their observations. In their study, Nitz and Capano used a different set of priors to assess the GW190521 signal than those originally used by LIGO–Virgo scientists.
LIGO–Virgo spots its most massive black hole merger so far
The duo’s work yielded two possible solutions. In the first, both masses were like those originally calculated by LIGO–Virgo. In the second, however, they fell well beyond the forbidden mass gap to either side: measuring roughly 166 and 16 solar masses. The heavier object would be an intermediate-mass black hole, which are thought to form not in supernovae, but by black holes devouring matter or even other black holes. These currently-elusive bodies lie between those formed by collapsed stars, and the supermassive black holes at the centres of galaxies – which can be millions or billions of times more masive than the Sun.
If Nitz and Capano’s interpretation is correct, it could not only resolve the mass gap mystery it would also make the GW190521 merger the first detected example of a stellar-mass body spiralling into an intermediate-mass black hole. Therefore, the duo’s results may offer compelling new clues about their properties of intermediate-mass objects and could enable astronomers to describe a greater variety of black hole mergers from future detections of gravitational waves.
The first black hole ever discovered is more massive than previously thought
The famed Cygnus X-1 black hole (illustrated, slurping mass off its companion star) is nearly 1.5 times as massive as astronomers thought, new observations suggest.
International Centre for Radio Astronomy Research
February 18, 2021 at 2:00 pm
The first black hole ever discovered still has a few surprises in store.
New observations of the black hole–star pair called Cygnus X-1 indicate that the black hole weighs about 21 times as much as the sun — nearly 1.5 times heavier than past estimates. The updated mass has astronomers rethinking how some black hole–forming stars evolve. For a star-sized, or stellar, black hole that massive to exist in the Milky Way, its parent star must have shed less mass through stellar winds than expected, researchers report online February 18 in Science.
Knowing how much mass stars lose through stellar winds over their lifetimes is important for understanding how these stars enrich their surroundings with heavy elements. It’s also key to understanding the masses and compositions of those stars when they explode and leave behind black holes.
The updated mass measurement of Cygnus X-1 is “a big change to an old favorite,” says Tana Joseph, an astronomer at the University of Amsterdam not involved in the work. Stephen Hawking famously bet physicist Kip Thorne that the Cygnus X-1 system, discovered in 1964, did not include a black hole — and conceded the wager in 1990, when scientists had broadly accepted that Cygnus X-1 contained the first known black hole in the universe (SN: 4/10/19).
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Astronomers got a new look at Cygnus X-1 using the Very Long Baseline Array, or VLBA. This network of 10 radio dishes stretches across the United States, from Hawaii to the Virgin Islands, collectively forming a continent-sized radio dish. In 2016, the VLBA tracked radio-bright jets of material spewing out of Cygnus X-1’s black hole for six days (the time it took for the black hole and its companion star to orbit each other once). Those observations offered a clear view of how the black hole’s position in space shifted over the course of its orbit. That, in turn, helped researchers refine the estimated distance to Cygnus X-1.
The new observations suggest that Cygnus X-1 is about 7,200 light-years from Earth, rather than the previous estimate of about 6,000 light-years. This implies that the star in Cygnus X-1 is even brighter, and therefore bigger, than astronomers thought. The star weighs about 40.6 suns, the researchers estimate. The black hole must also be more massive in order to explain its gravitational tug on such a massive star. The black hole weighs about 21.2 suns — much heftier than its previously estimated 14.8 solar masses, the scientists say.
The new mass measurement for Cygnus X-1’s black hole is so big that it challenges astronomers’ understanding of the massive stars that collapse to form black holes, says study coauthor Ilya Mandel, an astrophysicist at Monash University in Melbourne, Australia.
“Sometimes stars are born with quite high masses — there are observations of stars being born with masses of well over 100 solar masses,” Mandel says. But such enormous stars are thought to shed much of their weight through stellar winds before turning into black holes. The bigger the star and the more heavy elements it contains, the stronger its stellar winds. So in heavy element–rich galaxies such as the Milky Way, big stars — no matter their starting mass — are supposed to shrink down to about 15 solar masses before collapsing into black holes.
Cygnus X-1’s 21-solar-mass black hole undermines that idea.
The LIGO and Virgo gravitational wave detectors have discovered black holes weighing tens of solar masses in other galaxies (SN: 1/21/21). But that is probably because LIGO peers at distant galaxies that existed earlier in the universe, Joseph says. Back then, fewer heavy elements existed, so stellar winds were weaker. With the new Cygnus X-1 measurement, “now we have to say, hang on, we’re in a [heavy element]–rich environment compared to the early universe … but we still managed to make this really massive black hole,” she says, “so maybe we’re not losing as much mass through stellar winds as we initially thought.”
Questions or comments on this article? E-mail us at [email protected]
A version of this article appears in the March 13, 2021 issue of Science News.
What happens if a tiny and small black hole faces a heavier object like UY Scuti?
I couldn't find this explanation on any search that I've been digging, but I am pretty sure there is a very plausable one around.
We know that a black hole the size of a tennis ball would have at least the same mass and gravity as our planet, but let's wonder, if instead of Earth and moon we have a black 'tennis ball' hole and a Jupiter (heavier object) around?
We know that by standard physics, that bigger object attracts the smaller ones. So, if Jupiter locks this tiny black hole in its orbit and eventually the black hole is trapped by its inner gravity to the falling point of its magnetic fields, will the black hole just fall in Jups? And if so, what effects on both would be created? I simply can't get any idea out of this. The BH's event horizon surelly will keep trapping light with its "infinite density" beyond the point of no return, but if Jupiter is heavier than this Black hole I believe that the black hole wouldn't have strenght to maintain an event horizon to begin with. Of course this scenario is very unlikely to exist, but given the facts that we have black holes like the XTE (3,5 times the mass of our sun) what would happen if this XTE black hole could meet UY scuti (30 x the mass of the sun)?
A new way to search for black holes found an object heavier than the Sun
Astronomers have discovered a wide binary system of a bright star and an invisible massive object. According to modern concepts of companions, in this case can be only a black hole, which should be heavier than the Sun about 68 times. This makes it the largest known group of such objects, the mass of which is comparable to stellar.
Black holes are objects with such great gravity that nobody can move away from their immediate surroundings to infinity, even light. From the point of view of observation, there are three main types of such objects: black holes of stellar masses, intermediate masses and supermassive ones.
This classification reflects different formation mechanisms and different manifestations. In particular, all known until recently black holes of stellar masses (in addition to those recorded by gravitational waves) were discovered in X-ray binaries. In such systems, the substance of an ordinary star flows to a compact object, while heating up to millions of degrees and emitting high-energy radiation.
At the moment, all the black holes of stellar masses known in the Milky Way are no more than 20 times heavier than the Sun. This is in good agreement with the theory of stellar evolution, which describes the birth of such objects as a result of supernova explosions. At the same time, models predict that extremely heavy stars should end their lives in the form of paired unstable supernovae, after the explosions of which there is no compact object.
A team of Astronomers led by Liu Jifeng used a new way to search for black holes and discovered an object with a mass of about 68 solars in our galaxy. The authors used the radial velocity method, which is usually sought for exoplanets. To detect a body with its help, it is necessary to fix the periodic displacements of lines in the spectrum of a star, from which one can calculate the orbital and physical parameters of an invisible companion.
The search took place as part of a long-term spectroscopic binary observation program with the Chinese LAMOST telescope. In total, about 3,000 sources were studied in the direction of the anti centre of the Milky Way. One of the stars in this field, LB-1, showed periodic radial velocity variations, which were then independently confirmed by observations with other telescopes.
Accurate spectroscopic data made it possible to determine the parameters of the star with high accuracy. Its surface temperature is about 18,100 kelvin, the logarithm of gravity is 3.43, the mass is 8.2 solar, and the distance is 4.23 kiloparsecs. In its radiation, regular line shifts were found from periods of 78.3 days, which correspond to an amplitude of radial velocity of 52.8 kilometers per second.
This data is not sufficient to determine the mass of the companion since the angle of inclination of the plane of the orbit of the system relative to the line of sight is unknown. However, even in the case of a right angle, a mass of 6 solar is obtained, which already unambiguously classifies the object as a black hole. However, researchers have shown that the observed luminescence from the source in the H line α may not be associated with the visible star, disc or around the background object, because its width is 300 kilometers per second. Therefore, this radiation is associated with the disk around the black hole, which allows you to independently determine its mass, which corresponds to 68 solar with errors of about 12. It also allows you to determine the angle of inclination, which in this case is 15-18 degrees.
The object detected is exceptional in several ways. First, this is the heaviest directly discovered black hole in stellar masses. Secondly, it is part of the widest known double with a black hole in the composition, which is why it is not visible as an X-ray source. Thirdly, its mass is approximately two times higher than the limiting initial mass for black holes formed as a result of supernova explosions.
The restriction on the maximum mass of a black hole strongly depends on the metallicity of the original star, i.e., on the concentration of elements heavier than helium in it. However, LB-1 in this indicator corresponds to the Sun, from which approximately the same metallicity can be expected for the star-predecessor of the discovered black hole. In this case, at the time of formation, it should not have been heavier than 25 solar masses.
The authors suggest several possible scenarios for the formation of such an object. This black hole could have arisen after a hole with an allowed mass hit a large star about 60 times heavier than the sun. In this case, a significant proportion of the substance may be below the event horizon. Also, such an object could be formed after the merger of a pair of black holes that appeared after supernova explosions. In this case, the studied system should have initially been triple with a pair of very massive stars in close orbit. The authors do not exclude that this object can theoretically still be a very close system of two black holes with masses of about 35 solars.
Black star (semiclassical gravity)
A black star is a gravitational object composed of matter. It is a theoretical alternative to the black hole concept from general relativity. The theoretical construct was created through the use of semiclassical gravity theory. A similar structure should also exist for the Einstein–Maxwell–Dirac equations system, which is the (super) classical limit of quantum electrodynamics, and for the Einstein–Yang–Mills–Dirac system, which is the (super) classical limit of the standard model.
A black star doesn't need to have an event horizon, and may or may not be a transitional phase between a collapsing star and a singularity. A black star is created when matter compresses at a rate significantly less than the free fall velocity of a hypothetical particle falling to the center of its star, because quantum processes create vacuum polarization, which creates a form of degeneracy pressure, preventing spacetime (and the particles held within it) from occupying the same space at the same time. This vacuum energy is theoretically unlimited, and if built up quickly enough, will stop gravitational collapse from creating a singularity. This may entail an ever-decreasing rate of collapse, leading to an infinite collapse time, or asymptotically approaching a radius bigger than zero.
A black star with a radius slightly greater than the predicted event horizon for an equivalent-mass black hole will appear very dark, because almost all light produced will be drawn back to the star, and any escaping light will be severely gravitationally redshifted. It will appear almost exactly like a black hole. It will feature Hawking radiation, as virtual particle pairs created in its vicinity may still be split, with one particle escaping and the other being trapped. Additionally, it will create thermal Planckian radiation that will closely resemble the expected Hawking radiation of an equivalent black hole.
The predicted interior of a black star will be composed of this strange state of spacetime, with each length in depth heading inward appearing the same as a black star of equivalent mass and radius with the overlayment stripped off. Temperatures increase with depth towards the center.
- Carlos Barceló, Stefano Liberati, Sebastiano Sonego and Matt Visser, Scientific American (October 2009) Black Stars, Not Black Holes
- Barceló, C. Liberati, S. Sonego, S. Visser, M. (2008). "Fate of gravitational collapse in semiclassical gravity". Physical Review D. 77 (4): 044032. arXiv: 0712.1130 . Bibcode:2008PhRvD..77d4032B. doi:10.1103/PhysRevD.77.044032. S2CID20016596.
- Visser, Matt Barcelo, Carlos Liberati, Stefano Sonego, Sebastiano (2009) "Small, dark, and heavy: But is it a black hole?", Bibcode:2009arXiv0902.0346V, arXiv:0902.0346
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