from the drifting-falling-floating-weightless dept.
If, as astronomers believe, the death of large stars leave behind black holes, there should be hundreds of millions of them scattered throughout the Milky Way galaxy. The problem is, isolated black holes are invisible.
Now, a team led by University of California, Berkeley, astronomers has for the first time discovered what may be a free-floating black hole by observing the brightening of a more distant star as its light was distorted by the object's strong gravitational field — so-called gravitational microlensing.
The team, led by graduate student Casey Lam and Jessica Lu, a UC Berkeley associate professor of astronomy, estimates that the mass of the invisible compact object is between 1.6 and 4.4 times that of the sun. Because astronomers think that the leftover remnant of a dead star must be heavier than 2.2 solar masses in order to collapse to a black hole, the UC Berkeley researchers caution that the object could be a neutron star instead of a black hole. Neutron stars are also dense, highly compact objects, but their gravity is balanced by internal neutron pressure, which prevents further collapse to a black hole.
[...] "This is the first free-floating black hole or neutron star discovered with gravitational microlensing," Lu said. "With microlensing, we're able to probe these lonely, compact objects and weigh them. I think we have opened a new window onto these dark objects, which can't be seen any other way."
[...] Notably, a competing team from the Space Telescope Science Institute (STScI) in Baltimore analyzed the same microlensing event and claims that the mass of the compact object is closer to 7.1 solar masses and indisputably a black hole. A paper describing the analysis by the STScI team, led by Kailash Sahu, has been accepted for publication in The Astrophysical Journal.
(Score: 0) by Anonymous Coward on Thursday June 16 2022, @09:12PM (5 children)
If pieces where splattered out of a collision with another neutron star.
Are there limits to how this material is divided?
The black hole reported here is 7 solar masses, but is it possible to have a piece the size of a bacteria where it could be displayed in a museum under some kind of pyramid stand?
Curious if there are other pieces floating about waiting to be found at the center of an asteroid due to migration for example, or impact craters where there exists no actual meteoroid material.
(Score: 3, Informative) by Immerman on Thursday June 16 2022, @11:39PM (2 children)
If two neutron stars collided, I can't think of any particular limits on the fragments. I assume there'd be at least some, though it might just be a cloud of radiation and debris while the bulk merged together. The physics of the collision might have some really weird quantum-mechanical properties though, since (if I recall correctly) it's believed to be fairly common for most/all possible quantum states to have been filled by the intense forces of gravity, and the cores may actually be some sort of very strange quantum "liquid" rather than anything like we imagine solids (or more accurately atomic nuclei) to be.
For black holes - all collisions end in perfect mergers, they cannot fragment. But a sizable fraction of their combined mass can be emitted as gravitational waves during the final moments of their death-spiral. Which is why, despite the difficulty in detecting even fairly powerful gravitational waves, we can detect mergers in distant galaxies.
Size-wise, there is currently no theoretical lower limit to the mass of a black hole, though there's no known way for them to form at masses smaller than a star - at least not since the inflationary period at the beginning of the universe. Though it's generally assumed that as you get to the atomic scale quantum influences may start making it act weird, and at Plank-scales the granularity of space-time might set a lower limit.
More practically though, it's believed that small enough black holes will cease being black due to the immense amount of Hawking radiation they emit as they evaporate - the smaller the black hole, the greater the wattage emitted.
Near the extreme small end of primordial black holes that could still be around - one with a lifetime of 20 billion years would have a mass of 2.4x10^8 tons (about the same as a cube of water 620m on a side), be about half the size of a proton, and emit 6.3GW of radiation. Sort of like a point-source nuclear reactor that would last billions of years and emit crazy high-energy radiation (with a peak output at about 531,000 THz). That would be pretty easy to spot, would make an asteroid glow with anomalous heat (assuming the radiation didn't just pass right through it), and would be insanely useful if it could be harnessed. It would also be pretty much impossible for it to "eat" anything - between the sub-subatomic size and the insane radiation pressure, nothing could get anywhere close to the event horizon.
At a somewhat larger scale, a Ceres-mass black hole (9x10^17 tons) would be 0.27um across and only emit about 0.0004 uW. That would probably be able to devour an asteroid quite rapidly, in geologic terms at least.
However - there's an important consideration for any black-hole collision: the black hole is not going to stop. If a micro-black hole hits an asteroid it will cause an explosion of radiation as bits of the asteroid get annihilated in its path, leaving a potentially distinctive crater as superheated material continues to erupt out of the tunnel it leaves behind it. But there's nothing to slow the black hole itself down - it'd be far too tiny to absorb a significant amount of material to reduce its momentum, so it would just shoot out some other location on the the asteroid, leaving a very different crater in its wake, and continue on back into interstellar space (assuming it didn't get gravitationally captured by its interactions with the planets.)
About the only way you could get a black hole inside an asteroid is if the asteroid somehow formed around a black hole that had already been gravitationally captured in the solar system.
For more black hole fun, check out this calculator: https://www.vttoth.com/CMS/physics-notes/311-hawking-radiation-calculator [vttoth.com]
(Score: 0) by Anonymous Coward on Friday June 17 2022, @04:18PM (1 child)
After your response, it makes one think advanced civilizations will be on the hunt for this stuff, (harvestable sized gravity bodies)
For now, we can be on the hunt for this by looking for signs locally on Earth and the Moon or with other celestial bodies, maybe even vented signatures of spacecraft emissions.
Start with simulating the impact on the Moon with tiny blackhole or neutron fragments.
(Score: 2) by Immerman on Friday June 17 2022, @06:14PM
I seem to recall that we are in fact doing some preliminary hunts - if we managed to spot the double-"impact" of a black hole passing through the moon we could theoretically calculate its trajectory and go hunting for it. Assuming it was bound to the solar system we might even be able to catch it and put it to use as the core of space station. And as I recall, primordial micro black holes are in fact still in the running as potential contenders for dark matter - so there could potentially be huge numbers of them floating around.
Alternately, we could build them.
While there's no (post-inflation) known naturally occurring process that could create micro-black holes, there are some possibilities for doing so artificially.
All energy has the same mass (m=E/c^2), and while matter is normally far denser than other forms of energy, in theory an infinite number of photons can pass through the same point in space simultaneously. A powerful enough pulse of synchronized photons at a tiny point and you *should* create a black hole. Of course we're still talking about energy equivalent to doing a complete matter-energy conversion of the huge mass required, and having all the photons hit the same point simultaneously... that could be a real challenge. And accidentally creating a smaller than intended black hole would be catastrophic as it would effectively slowly detonate with all the power of a star.
An easier option might be a super-massive Bose-Einstein condensate. Helium is the smallest naturally occurring (in significant quantities) atomic boson, with a covalent radius of 28pm (x10^-12m). Condense at least 1.9x10^13 tons of it into a single atomic radius and you should get a black hole. Of course helium is pretty rare, it might be easier to use something else. Oxygen is the next smallest at 66pm, and extremely abundant pretty much everywhere in the universe. That'd need 4.4x10^13 tons.
Unfortunately even the helium version would be too large to emit much Hawking radiation - only about 1 watt, while the oxygen version emits about 1/5 of a watt. However, you could still use them as mass-energy converters: feeding them carefully should allow you to convert almost 50% of the matter into radiation that escapes to be captured as energy.
There is another possibility though - while the radius of an oxygen *atom* is 66pm, basically all of the mass is in the nucleus, which has a radius of only only 28x10^-16m. If you assume the nuclei are in fact all concentrated at the center of a sufficiently dense Bose-Einstein condensate, as you'd naively expect - then you would only need about 1.9 billion tons of oxygen to hit a critical mass density. A black hole that size would emit 100MW for trillions of years.
(Score: 0) by Anonymous Coward on Friday June 17 2022, @10:15AM (1 child)
Nope, not enough gravity to keep the thingy together. It will fly out in smaller fragments, decaying in normal matter
(Score: 2) by Immerman on Friday June 17 2022, @06:41PM
Oh? Could you point me at the theory behind that so I can read further?
It's definitely necessary to have insane gravity to *create* "neutronium" - but once created you've essentially got an insanely large atomic nucleus with atomic number 0.
Remove it from the insane gravitational well and it might well begin undergoing nuclear decay - but I don't believe we have the ability to even begin to predict the potential stable states of a nucleus containing zillions of nucleons - nor to say that they don't exist. We might have the theory (though it's probably dangerous to assume our theory is accurate enough to predict behavior that far beyond the scale it was developed for), but I suspect it's rather like chemistry - where we have the theory to predict the behavior of chemical compounds, but in practice the math is so complicated that we don't have the computational power to predict the behavior of anything more complex than the simplest H2 molecule.
(Score: 2) by legont on Friday June 17 2022, @01:16AM
Apparently there was matter spread out through the universe. It got condensed into bulbs by gravity. If they were big enough they would light up as stars. Small ones become planets. Yes, including the free flown ones. They got to be the most common objects out there. Our star is somewhat bigger than usual and there are 3 planets that did not grow fast enough to become stars. We could have 2-4 star system. Or we could have a giant that would burn fast and become a neutron star or even a black hole. The difference in mass is not even that much.
This is all random. Well, the distributioon may or may not be complicated but we should expect all the variants. What is interesting is the distribution but it is a pure math task. Yes, I realize that we don't have this math yet.
"Wealth is the relentless enemy of understanding" - John Kenneth Galbraith.