However there is an update to the article posted today:
[Update: On September 2, 2020, researchers confirmed [1] that the colliding black holes had masses 65 and 85 times that of our sun. The resulting black hole was 150 times more massive than the sun.]
It was less "should not exist" and more "should only form when black holes merge," and apparently the "black hole mergers fill the mass gap" hypothesis is now supported by evidence. Nobody was claiming that there is some physical reason black holes of such mass could not exist, only that the best understood process of black hole formation should not allow for such masses (but other processes can).
> Chris Belczynski, an astrophysicist at Warsaw University, previously felt so sure that such a large specimen wouldn’t be seen that in 2017 he placed a bet with colleagues. “I think we are about to lose the bet,” Belczynski said, “and for the good of science!”
LIGO has existed for decades and by 2017 had already detected a merger. My guess is he considered black holes in this range rare enough that we were unlikely to detect any. If he believed they were impossible the article certainly doesn’t elucidate on that fact.
I presume that different masses of black holes result in different frequency waves, and that LIGO is not uniformly sensitive to all frequencies. Depending on the actual numbers, this would make these intermediate sized mergers either over or under represented in our data.
Somehow black hole videos have ended up at the top of my youtube recommendations lately, and it seems like the binary star system is a somewhat common path to supernovae or black holes. And we know about some trinary and double binary systems out there.
I would think after supernova, the companion star(s) would end up in a modified orbit that would result in more destructive gravitational interactions (collisions, mass transfer, feeding or creating a black hole). To the layperson it feels like a matter of 'when', not 'if'.
Perhaps it's that I'm thinking that in a universe of a billion billion distinct examples of orbital mechanics, surely we are going to spot a lot of exceedingly lucky/unlucky events out there. Especially if we are doing any kind of observation that filters for those events.
After all, a one-in-a-billion probability event on earth happens to about eight people. If you know how to find them, it's a good human interest story.
Would there be a reason we wouldn't expect these mergers to happen very often? I mean, LIGO doesn't detect black holes that often considering how much space it is surveying. Would there be time for the small black holes to accumulate into a large black hole?
LIGO only detects mergers, and then only in a certain low mass range. The article hints that these are most likely to happen in a star-dense area (duh, right?) like a nebula.
Yeah I think the key words in the bet, were "astrophysical" black hole coming from a star, as opposed to "dynamical" ones coming from mergers. It seems the party doubting dynamical ones thought space was big and they would be unlikely to find each other. As evidence is showing, all kinds of mergers are happening.
> For cores with a mass between about 65 and 130 times that of our sun (according to current estimates), the star is completely obliterated [via a pair-instability supernova]. Cores between about 50 and 65 solar masses pulsate, shedding mass in a series of explosions until they drop below the range where pair instability occurs. Thus there should be no black holes with masses in the 50-to-130-solar-mass range.
> The million- and billion-solar-mass supermassive black holes that anchor galaxies’ centers formed differently, and rather mysteriously, in the early universe. LIGO and Virgo are not mechanically capable of detecting the collisions of supermassive black holes.
When two black holes with a near-circular orbit and similar size merge, they should both be going close to the speed of light about their common center shortly before the merge. (Right?) Do close orbits tend to become more, or less, eccentric?
After the event horizon surfaces contact, does it become spherical in minimal time, or does it keep a complicated shape for an extended period? (E.g., until gravitational waves carry off enough energy?) And does the very large rotational momentum affect properties of the resulting black hole?
I'd think binary systems made up of similarly sized objects where the orbits are in some sense "close" are almost by definition not eccentric. To get to that point from a previously eccentric orbit they convert the eccentricity to spin. Check out this out for an example with neutron stars: https://www.youtube.com/watch?v=-JZBmgOEfdo
As to the second part, I'd think it becomes axially symmetric in very minimal time. I don't have a good answer as to why, except that my intuition says the GW signature of blackhole mergers at the point of the merger has a frequency that appears to get infinitely fast as it radiates away the axial asymmetry.
While this is interesting, the article and graph within are misleading and clickbaity.
This black hole is big enough to fall into a mass RANGE that shouldn't exist, but isn't the largest found (which I feel the title of the article implies).
Supermassive black holes are on the scale of BILLIONS of solar masses.
Doesn't really make sense that the range wouldn't exist either, unless I'm confused.
Obviously black holes are colliding otherwise we probably wouldn't have supermassive black holes, so it doesn't seem unexpected that two smaller black holes would collide and form one bigger than the limit imposed by pair-instability supernova, except as a statistical improbability.
It's not clear how the gap between solar-mass scale black holes and supermassive black holes was traversed; was it a build up from small black holes, or did they start out as seeds of a few million solar masses in the early universe? What about the dearth of intermediate sized black holes (tens of thousands of solar masses)? Is this just because they are just hard to see to begin with, or is there really a gap? This is intimately related to the Salpeter time, which is how long it takes to grow black holes if they accrete at the Eddington limit, and can also be inferred from the quasar luminosity function. IIRC this favors the massive seed scenario, but there's no shortage of clever explanations around it.
Black holes get less dense as they gain mass - assuming I didn't drop a factor of 2 or τ, a 1 solar mass black hole has a density of 147 quadrillion tons per cubic meter. A black hole of 100 million solar masses had density of only 14.7 tons per cubic meter (for reference, lead is 11.3 Tn/m3 and osmium is 22.6 Tn/m3). So a sphere of 100M (actually >81M) solar masses of osmium would collapse into a black hole without even having to compress under it's own gravity first. You'd need 384 million solar masses for something with the density of water.
LIGO and VIRGO are sensitive to gravitational waves within a specific frequency range. The bulk of GW energy is emitted at a frequency that is twice the orbital frequency of the objects emitting the gravitational waves. Supermassive black holes are sufficiently large that they merge before they could have an orbit compact enough to emit gravitational waves at high enough frequencies for LIGO and VIRGO to detect them. Less massive compact objects are smaller and so can reach higher orbital frequencies before merging.
The low frequency noise is very bad for ground-based gravitational-wave interferometers. For example, seismic noise from ground motion, such as waves hitting the west coast for LIGO Hanford, or logging operations for LIGO Livingston; also the control noise is really bad at low frequencies. Generally most noises apart from the quantum noise scale inversely to the frequency.
The ground-based detectors are most sensitive at 100Hz, which is around the frequency of the binary black hole inspiral. Supermassive black holes are more like millihertz. We do not have any concrete way yet to measure the gravitational waves from supermassive black holes, but there are some ideas. For example we can look at the time dilation of frequencies of nearby pulsars (https://en.wikipedia.org/wiki/Pulsar) as a kind of gravitational wave interferometer in space, however to get a signal-to-noise ratio greater than one many years (decades) of data is needed.
Your reasoning is on the right track, but it's the wavelength specifically that's outside of the range for both Virgo and LIGO. As far as I understand the subject, we're running into physical limits for their detection using that kind of experiment. Instead, research is attempting to infer the mergers using pulsar Doppler shift measurements.
No. In fact, the entire observable universe is a black hole: the Schwarzschild radius of the mass of the observable universe is greater than the observable size, meaning by the technical definition of a black hole we are living within one: light from Earth sent into the darkest region of the sky will not escape the gravitational pull of the whole universe, even before considering expansion rates.
The Schwarzschild radius for the mass of the observable universe is about 13.7 Billion Light Years while the observable universe is about 93 Billion Light Years across (radius ~46 Billion Light Years). So the universe is not itself a black hole (until you take expansion rates into account)
I think you have that backwards--you have to take expansion into account for the "observable" universe to be that large, since the age of the universe is only 13.7 billion years.
Your guess is correct. The signature is very different.
In order to reach LIGO's frequency band, the objects must be very compact. If they are too large, they touch before they can orbit each other at sufficiently-high (audio!) frequencies.
The Schwarzschild radius of the black holes in question are less than 100km in size, while the size of a star as small as our Sun is ~700,000 km in size.
Moreover, the compact objects (neutron stars, black holes) that LIGO can observe are exceptionally dense ( > 3x10^17 kg/m^3), while stars have roughly the density of water (1000 kg/m^3) on average, and much less at their extremities. Compact objects can disrupt nearby stars long before they could touch, spreading the "merger" across many, many years (many, many millenia, I suspect), rather than the fraction-of-a-second typical of a LIGO black-hole observation.
What state that supermassive star would be? If it is red giant, black hole would dissasemble and strip it right away. For black hole gravitation pull red giants are just some gases in the neighbourhood
Absolutely, the question was only how frequently it happens. The bet was within the first 100 detections — with one side only saying they're rarer than that.
https://news.ycombinator.com/item?id=20819902
However there is an update to the article posted today:
[Update: On September 2, 2020, researchers confirmed [1] that the colliding black holes had masses 65 and 85 times that of our sun. The resulting black hole was 150 times more massive than the sun.]
[1] https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.12...