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The gravitational wave detectors are turned on again and we are turned on



The LIGO Hanford Observatory
Photo: Ligo (RIT)

The gravitational wave detectors from LIGO and Virgo will continue their search for gravitational waves on April 1. This will be much more sensitive thanks to a series of upgrades for lasers, mirrors and other components. This next round will be a big deal for a variety of reasons. The first two observation sessions.

We have officially entered an era in which two black holes collide in an unfathomable collision that can actually see waves hurling through space-time – is "routine." But most of the individual collisions do not worry the scientists anymore. Instead, they are generally interested in the behavior of our universe – how black holes can collide, which places in the universe harbor these kinds of black holes, and whether black holes grow through a kind of chaotic family tree.

"We expect dozens of events in our upcoming observation run," said Christopher Berry, CIERA research professor at Northwestern University, to Gizmodo. "It could really dramatically change the knowledge about the population of black holes."

Short summary: Albert Einstein first theorized that gravity should move at the speed of light, as the waves themselves rippled through space (and time). After decades of targeted searches, the scientists finally announced in 2016 that they had discovered the waves that had emerged from two colliding black holes in two several-kilometer L-shaped tunnels, each with a laser beam. Special mirrors split the laser beam into two parts, sending the parts through the two wings of the tunnel and uniting them on a detector. The detector detected the incredibly small waves in space-time as the lasers moved in and out of phase.

The detectors have now measured 10 cases of black holes and two neutron stars, incredibly dense objects around the mass of the Sun, but as big as a small city beating together. But capturing only gravitational waves is no longer the most interesting piece. Well, these detectors serve essentially the same purpose as telescopes, but measure gravity instead of light.

Scientists have all sorts of questions. In which environments, for example, are there mature conditions for bringing two black holes close together? There are two competing ideas, and either (or maybe both) might be right. Perhaps pairs of black holes are made up of double stars, both of which invade black holes. Or maybe there are regions in the universe that are thick with black holes and close enough to collide. Astrophysicists can deduce whether the spins of the black holes were aligned or misaligned during a collision based on the resulting gravitational waves, a value with which they can find out how they formed.

A related question is whether black holes grow. The most recent data dump of the gravitational wave detectors contained a black hole called 170729, which is 80 times the solar mass and is larger than is known when a star collapses. The researchers therefore wondered if black hole mergers are only part of the black hole life cycle. Do black holes have pedigrees and grow and double as more mergers take place? A recent paper by university student Chase Kimball at Northwestern University and Berry and Vicky Kalogera has attempted to determine the likelihood that GW170729 is indeed a second generation black hole, the result of two mergers, provided there are many globular clusters Black holes live together.

Your result: It is possible, but more data is needed. And that makes the restart of the US-American LIGO and the Italy-based Virgo reboot so exciting.

"We're basing the total number of black holes based on 10 binary black holes," Kimball said. "I'm excited, because if we can do this out of ten black holes, [on April 1] the third observation run will start, and we'll see many more." Scientists can see so many 40 black hole collisions during this run.

If you think about it, we are broadening our understanding not just from black holes, but from stars themselves. When stars, as bright nuclear fusion powerhouses, have reached their end, the stars do not just wallow as dark star bodies – they could enjoy a rich, vibrant second life by blending and growing black holes. It's difficult to say.

"This part of the massive stellar evolution has not been observed before," said Maya Fishbach, Ph.D. student at the University of Chicago, Gizmodo. She agreed that the answer to these questions is possible only with more events.

Where do the scientists get the idea that they will see so many more events? Well, on the last observation run, scientists will be able to see three times more of the universe than in the last run, said Will Farr, astrophysicist at Stony Brook University and the Simons Foundation Flatiron Institute, opposite Gizmodo. Not only could this bring about dozens more events, there could also be surprises that researchers did not expect. There could also be more neutron star mergers that could help us better understand the origins of elements like gold or the mysterious outbreaks of gamma rays that scientists sometimes discover. Whatever happens, it will be exciting and we are curious to see how the data comes.


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