If you’ve ever been to a park that’s home to bears, you’ve seen signs warning not to get close to them and not to feed them. Despite that, people still try to get close to bears and feed them. Would it help if the sign showed a video of a bear eating one of these sign-ignoring humans? You’ve probably heard that black holes consume everything in sight and it would be dangerous to get too close, yet you can just imagine a space explorer and Kirk wannabe ignoring those warnings. Would it help if they could watch a black hole eating one of the densest objects in the universe? How about two of them? Well, now they can. Will it help?
“It was just a big quick (gulp), gone. (It) gets a nice dinner of a neutron star and makes itself just a little bit more massive.”
In terms even the dimmest bulb on a starship approaching a black hole can understand, Patrick Brady, an astrophysicist at the University of Wisconsin Milwaukee, describes to AP News what he and other astronomers observed twice in a span of about a week, making them the only humans to ever witness the ‘collision’ of a black hole and a neutron star – which is a dead star that didn’t become a black hole. This is something that team member Chase Kimball, a graduate student at Northwestern University and co-author of the study published in the Astrophysical Journal Letters, tells NPR occurs roughly every 30 seconds somewhere in the observable universe, and once a month in space one billion light years from Earth. The key is knowing where to look with the right equipment.
“We report the observation of gravitational waves from two compact binary coalescences in LIGO’s and Virgo’s third observing run with properties consistent with neutron star–black hole (NSBH) binaries. The two events are named GW200105_162426 and GW200115_042309, abbreviated as GW200105 and GW200115; the first was observed by LIGO Livingston and Virgo and the second by all three LIGO–Virgo detectors.”
In these cases, the ‘right equipment’ are the two gravitational wave detectors comprising LIGO (Laser Interferometer Gravitational-Wave Observatory) and the Virgo interferometer, another wave detector. Both LIGO Livingston (Louisiana) and Virgo picked up the signal from the first black hole/neutron star merger on January 5, 2020 (GW200105), which appeared to be a black hole of about nine solar masses and a neutron star of about 1.9 solar masses about 900 million light years away. All three detectors picked up the second one (GW200115) on January 15, involving a black hole of six solar masses and a neutron star of about 1.5 solar masses. While their masses were huge, the neutrons stars were extremely dense, putting their physical size about that of a large city.
“These were not events where the black holes munched on the neutron stars like the Cookie Monster and flung bits and pieces about. That ‘flinging about’ is what would produce light, and we don’t think that happened in these cases.”
Co-author Patrick Brady of the University of Wisconsin-Milwaukee, spokesperson of the LIGO Scientific Collaboration, warns starships thinking about getting close enough to a black hole to pet it that they will not have time to even scream because it won’t be chomping down – it will be gulping down whole like a frat boy in a chugging contest. Co-author Maya Fishbach, also from Northwestern, told Ars Technica that seeing these events doesn’t mean they know where to look for more … at least not yet.
“With future gravitational wave data, we will have the statistics to answer these questions, and ultimately learn how the most extreme objects in our universe are made.”
Future starships should consider taking these astronomers along on missions. At least they know where to look to watch what happens when you ignore the black hole warning signs.