Seven years ago, researchers at the Laser Interferometer Observatory (LIGO) reported the first detection of gravitational waves. Now, the list of gravitational wave candidates is nearly 100.
And astronomers are confident that they can find more of these ripples in the fabric of space-time, which are caused by the acceleration of massive objects – for example, two black holes They spiral towards each other for a catastrophic fusion.
May 24 marked Monitor start-up 4 (O4), the latest effort of the LIGO-Virgo-KAGRA (LVK) collaboration. With newly upgraded gravitational-wave detectors, astronomers hope O4 can see gravitational waves – and the things you produce – a daily occurrence.
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“We expect to pick up from what we had in our previous run – one neutron star Every two months, one [binary] “A black hole every week or 10 days,” said Salvatore Vitale, an MIT astrophysicist, “getting a binary black hole every day or two, getting a neutron star every week.”
Gravitational waves are a byproduct of general relativityas envisioned before Albert Einstein a century ago. General relativity says that space and time are like a tapestry. Each object leaves a dent in this texture, which we perceive as attractive. In this world, turbulence — such as the collision of two black holes — can send ripples through the fabric. Astronomers can use laser-based detectors to spot these ripples.
As LVK’s name suggests, the collaboration is a multi-pronged effort, bringing together four detectors on three continents: legoTwo detectors, one in Livingston, Louisiana and one in Hanford, Washington. Virgo in Europe, extending across the Tuscan plains southeast of Pisa, Italy; And kajraUnder the mountains of central Japan.
Sadly, as O4 starts, only the LIGO pair is fully functional. Virgo It must undergo repairs to a corrupted mirror and will remain inactive for an uncertain period of time. KAGRA, meanwhile, will notice for just one month before going offline again; It did not reach its target sensitivity, and its operators hope to restart it again in late 2024.
Astronomers want more detectors because a single gravitational-wave detector doesn’t provide details about which direction the waves are traveling. So, they need multiple detectors to triangulate the source of the gravitational waves. With all four, astronomers can trace a source to a few square degrees of the sky. With only two detectors, they’re stuck with a wedge much larger than the sky.
“It would be difficult for us to tell our telescope friends where to point their telescope,” said Vitali.
But even two detectors can yield a lot of science. As sensitivity increases, detectors can pick up weaker or farther away gravitational waves. This means that scientists can capture more events.
And with more events, they hope to start answering a looming question: Where do the black holes they see form?
Black holes may have formed inside galaxies. You may be out there, in globular clusters or dwarf galaxies. Or perhaps they are primordial, having formed in the raw space of the early universe.
“To answer this question, you have to have a big data set,” said Vitali.
LVK stream Schedule It calls for O4 to run for 18 months, through 2025. After that, the gravitational-wave detectors will be shut down for upgrades and engineering work — and they’ll start up again around 2027 for five, a longer observational period.
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