
Possible detection of a black hole with a mass thought to be impossible - pseudolus
https://www.quantamagazine.org/a-black-hole-so-big-it-should-not-exist-20200902/
======
merricksb
Discussion about this article last year:

[https://news.ycombinator.com/item?id=20819902](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...](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.101102)

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betterunix2
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).

~~~
cgriswald
The title is bad, but...

> 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.

~~~
3JPLW
This was a key feature of the bet. It's within the first 100 gravitational
wave detections. They're betting against an unknown distribution.

Neither side was saying that they wouldn't be found.

~~~
gizmo686
Is there a sampling bias involved?

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.

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brundolf
> 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.

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ncmncm
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?

~~~
Enginerrrd
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](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.

~~~
ncmncm
Thank you. Searching for "Hypermassive Neutron Star" turns out to be very
informative.

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mmazing
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.

[https://en.wikipedia.org/wiki/List_of_most_massive_black_hol...](https://en.wikipedia.org/wiki/List_of_most_massive_black_holes)

~~~
fastball
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.

~~~
graerg
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.

~~~
a1369209993
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.

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thunderrabbit
Why are LIGO and Virgo not mechanically capable of detecting the collisions of
supermassive black holes?

Is it because the amplitude is so big it "pegs the needle" above its limit?

~~~
privong
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.

~~~
7373737373
There seem to be projects for lower frequencies/longer wavelengths underway:
[https://youtu.be/GlmMxmWHEfg?t=3733](https://youtu.be/GlmMxmWHEfg?t=3733)

~~~
thunderrabbit
Cool!

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moralestapia
Is there an "upper" limit on the mass of a black hole?

I would guess "no" but then again I'm not a physicist, maybe there's a
surprise down the road.

~~~
garmaine
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.

~~~
ptspin
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)

~~~
garmaine
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.

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wizardforhire
I’d like to point out and give props to this article for providing a picture
of the actual hand written bet that led to this research!

Humorous and rarely shared in science articles and gives some great context
for the personalities involved!

<3s!!!

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DrBazza
142 solar mass black hole:
[https://www.ligo.org/detections/GW190521.php](https://www.ligo.org/detections/GW190521.php)

~~~
3JPLW
Yes, that was this event.

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pantulis
what's the reason for discarding a merger between, say, a black hole and a
supermassive star? I guess then the wave signature would be different.

~~~
ISL
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.

For a visual image of the interaction of a large/fluffy star with a compact
object, have a gander at a few of these images:
[https://www.google.com/search?q=roche+lobe+accretion](https://www.google.com/search?q=roche+lobe+accretion)

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jagger27
Well that was a silly bet. Of course we were bound to find something in
between a just formed black hole and a supermassive black hole.

~~~
3JPLW
> Of course we were bound

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.

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scns
off topic but still "Impossible is Nothing" by Divine Heresy for nerds who
like Metal:
[https://www.youtube.com/watch?v=VFeoVCFdQ6k](https://www.youtube.com/watch?v=VFeoVCFdQ6k)

