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posted by martyb on Saturday July 11 2020, @06:18PM   Printer-friendly
from the a-proton-and-a-neutron-walk-into-a-black-hole dept.

Scientists propose plan to determine if Planet Nine is a primordial black hole:

Dr. Avi Loeb, Frank B. Baird Jr. Professor of Science at Harvard, and Amir Siraj, a Harvard undergraduate student, have developed the new method to search for black holes in the outer solar system based on flares that result from the disruption of intercepted comets. The study suggests that the LSST[*] has the capability to find black holes by observing for accretion flares resulting from the impact of small Oort cloud objects.

"In the vicinity of a black hole, small bodies that approach it will melt as a result of heating from the background accretion of gas from the interstellar medium onto the black hole," said Siraj. "Once they melt, the small bodies are subject to tidal disruption by the black hole, followed by accretion from the tidally disrupted body onto the black hole." Loeb added, "Because black holes are intrinsically dark, the radiation that matter emits on its way to the mouth of the black hole is our only way to illuminate this dark environment."

[...] The upcoming LSST is expected to have the sensitivity required to detect accretion flares, while current technology isn't able to do so without guidance. "LSST has a wide field of view, covering the entire sky again and again, and searching for transient flares," said Loeb. "Other telescopes are good at pointing at a known target, but we do not know exactly where to look for Planet Nine. We only know the broad region in which it may reside." Siraj added, "LSST's ability to survey the sky twice per week is extremely valuable. In addition, its unprecedented depth will allow for the detection of flares resulting from relatively small impactors, which are more frequent than large ones."

[*] LSST:

The Vera C. Rubin Observatory, previously referred to as the Large Synoptic Survey Telescope (LSST), is an astronomical observatory currently under construction in Chile. Its main task will be an astronomical survey, the Legacy Survey of Space and Time (LSST). The Rubin Observatory has a wide-field reflecting telescope with an 8.4-meter primary mirror that will photograph the entire available sky every few nights. The word synoptic is derived from the Greek words σύν (syn "together") and ὄψις (opsis "view"), and describes observations that give a broad view of a subject at a particular time. The observatory is named for Vera Rubin, an American astronomer who pioneered discoveries about galaxy rotation rates.

Journal Reference:
A. Siraj, A. Loeb. Searching for Black Holes in the Outer Solar System with LSST, https://arxiv.org/abs/2005.12280v2


Original Submission

 
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  • (Score: 4, Interesting) by Anonymous Coward on Saturday July 11 2020, @09:29PM (5 children)

    by Anonymous Coward on Saturday July 11 2020, @09:29PM (#1019665)

    You can make a black hole of any size. You just have to squeeze it down to smaller than the Schwarzschild radius for the amount of mass you are using. r = 2GM / c2 . The gravitational constant G is pretty small and c2 is pretty big, so that makes r really tiny unless M is huge.

    Black holes emit Hawking radiation in inverse proportion to their size, so small ones radiate faster, leading to a runaway effect where little ones go bang. Practical minimum size is about a planetary mass. A lunar mass one would be in rough equilibrium with outgoing Hawking radiation matched with CMB radiation falling in.

    Theory says any number of them of all sizes could have been formed during the big bang, but the counterargument is that we should be seeing occasional unexplained explosions as the smaller ones hit the runaway point. Astronomy has yet to detect any such explosions.

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  • (Score: 1) by khallow on Sunday July 12 2020, @04:40AM

    by khallow (3766) Subscriber Badge on Sunday July 12 2020, @04:40AM (#1019728) Journal
    On the other side of the coin, large massive objects like stars should be catching a fair number of these things. Even if it's rare today, it'd be a much more common thing in the early universe (as a combo of a denser universe and more primordial survivors).
  • (Score: 2) by Opportunist on Sunday July 12 2020, @10:50AM (3 children)

    by Opportunist (5545) on Sunday July 12 2020, @10:50AM (#1019788)

    The problem is the "squeeze it down" part. Normal black holes (well, as normal as objects as crazy as these can be) do this by gravity, but with such small ones, gravity alone won't cut it. So what squeezes them down?

    • (Score: 0) by Anonymous Coward on Sunday July 12 2020, @11:55AM (2 children)

      by Anonymous Coward on Sunday July 12 2020, @11:55AM (#1019806)

      The Big Bang supposedly had sufficient pressure to do it in the first few micro? milli? seconds. Not for long anyway. Hence primordial - nothing since has made small black holes, except possibly some Kardeshev II or III aliens.

      • (Score: 2) by Opportunist on Sunday July 12 2020, @05:33PM (1 child)

        by Opportunist (5545) on Sunday July 12 2020, @05:33PM (#1019912)

        And one of those superspecialawesome black holes made it to our solar system? Erh... yeah.

        • (Score: 0) by Anonymous Coward on Sunday July 12 2020, @06:01PM

          by Anonymous Coward on Sunday July 12 2020, @06:01PM (#1019929)

          Not really my field but as I understand it, if it made any at all then the Big Bang should have made lots of them. If there were lots of them then we should see more gravitational lensing events. We don't, so people tend to assume that there were none.