The strange behavior of a galaxy about a billion light-years away suggests it could be hosting one of the most anticipated events in modern astronomy.
Fluctuations in light from the center of the galaxy SDSS J1430+2303 look suspiciously like a pair of supermassive black holes with a combined mass of about 200 million suns that are about to collide with each other.
In cosmic terms, ‘threatening’ can often span entire lives. Fortunately, in this case, astronomers predict that if the signal is indeed the result of colossal black holes, they will merge within three years.
It may be our best chance yet of seeing two supermassive black holes collide… but we’re still not sure if that’s what’s happening at the heart of J1429+2303. Scientists advise that we continue to look at the strange galaxy to see if it can be definitively identified.
The first detection of colliding black holes in 2015 ushered in a bold new era for astronomy. Since then, many more detections have been made thanks to the gravitational waves that send these massive events through space-time.
To date, almost all of these mergers have been binary pairs of black holes with masses comparable to individual stars. There is a very good reason for this. LIGO and Virgo, the gravitational wave instruments responsible for the detections, are designed for this mass range.
The heavier ripples generated by inspiring and colliding supermassive black holes, in the range of millions to billions of times the mass of the Sun, are in a frequency range too low for our current observatories.
Still, the merging of a pair of supermassive black holes would be a damn sweet thing to observe. Even without a detector capable of detecting low-frequency gravitational wavesscientists expect to see an immense burst of light across the spectrum.
The data packed into that eruption can tell us so much about how these events unfold. We’re not entirely sure how supermassive black holes get that big, but there’s some evidence that binary mergers are a mechanism.
We know that galaxies have supermassive black holes at their centers, and we have observed not only pairs and groups of galaxies colliding, but supermassive black holes orbiting each other in reciprocal decaying orbits at the centers of these galaxies after the merger. These are derived from oscillations in the light emitted from the galactic center of these galaxies, on regular timescales that suggest orbits.
This brings us back to J1430+2303. Earlier this year, a team of astronomers led by Ning Jiang of the University of Science and Technology of China uploaded a paper to preprint server arXiv describing some very strange behavior. Over a period of three years, the oscillations in the galactic core became shorter and shorter, from a period of about a year to just a month.
However, it’s not entirely clear that what’s happening at the heart of J1430+2303 is the result of a binary black hole, let alone one about to kaboom. Galactic nuclei are strange places, they send out signals that are difficult to interpret, meaning it’s possible that something else is causing the variability in the heart of J1430+2303.
To get to the bottom of matter, astronomers turned to X-ray wavelengths. Using data from a series of X-ray observatories spanning a period of 200 days, a team led by Liming Dou of Guangzhou University in China has attempted to identify high-energy signatures that we would expect to see in a nearby supermassive black hole. binary on a rotting orbit.
They saw variations in the X-ray light emitted from the galaxy, as well as a type of emission associated with iron falling on a black hole, which the team detected with a 99.96 percent confidence level from two different instruments. This emission can be associated with binary supermassive black holes; however the team could not measure the “smoking gun” characteristics that would confirm a binary black hole.
The analysis of the radio observations published in July was also inconclusive. So it seems we’re still not 100 percent sure about what’s happening with J1430+2303.
What we can say with confidence is that something very strange seems to be happening at the center of the galaxy. Above all, it is a mystery, and a very juicy one; whether it’s a supermassive black-hole binary on the verge of a collision or not, J1430+2303 seems to deserve closer, more detailed attention.
The article has been accepted for publication in Astronomy and Astrophysicsand is available on arXiv.