The strange behavior of a galaxy billions of light-years away suggests that it may be home to one of the most anticipated events in modern astronomy.
Fluctuations in light from the galaxy’s center, SDSS J1430+2303, appear suspiciously like a pair of supermassive black holes with a combined mass of around 200 million Suns on the verge of colliding.
In cosmic terms, “imminent” can often last for lifetimes. Fortunately, astronomers predict that if the signal is caused by colossal black holes, they will merge within the next three years.
It could be our best chance yet to witness the collision of two supermassive black holes… But we’re not sure if that’s what’s going on at the heart of J1429+2303. Scientists advise that we keep an eye on the strange galaxy to see if it can be definitively identified.
The discovery of colliding black holes in 2015 marked the beginning of a bold new era in astronomy. Many more detections have been made since then, thanks to the gravitational waves sent rippling through space-time by these massive events.
Almost all of these mergers have so far involved binary pairs of black holes with masses comparable to individual stars. This is for a very good reason. The gravitational wave detection instruments, LIGO and Virgo, are designed for this mass range.
The more ponderous ripples produced by inspiralling and colliding supermassive black holes, with masses ranging from millions to billions of times that of the Sun, are too low for our current observatories to detect.
Still, observing the merger of two supermassive black holes would be a freaking treat. Even in the absence of a detector capable of detecting low frequency gravitational waves, scientists anticipate a massive outburst of light across the spectrum.
The information packed into that outburst could reveal a lot about how these events unfold. We don’t know exactly how supermassive black holes grow so massive, but there are a few hints that one mechanism is binary mergers.
We know that galaxies have supermassive black holes in their centers, and we’ve seen supermassive black holes circling each other in mutual, decaying orbits in the centers of these post-merger galaxies, not just pairs and groups of galaxies colliding. This returns us to J1430+2303. Earlier this year, a group of astronomers led by Ning Jiang of the University of Science and Technology of China published a paper on the preprint server arXiv describing some unusual behavior. Over a three-year period, the oscillations in the galactic nucleus became shorter and shorter, from about a year to just one month.
However, it’s not entirely clear that what’s going on at the heart of J1430+2303 is the result of a black hole binary at all, let alone one on the verge of exploding. Galactic nuclei are strange places, emitting signals that are difficult to interpret, implying that something else could be causing the variability in J1430+2303.
Astronomers used X-ray wavelengths to try to get to the bottom of the problem. A team led by Liming Dou of Guangzhou University in China attempted to identify high-energy signatures that we would expect to see in a close supermassive black hole binary on a decaying orbit using data from a variety of X-ray observatories over a 200-day period.
Radio observations analyzed in July were also inconclusive. So it appears that we are still unsure about what is going on with J1430+2303.
What we can say with certainty is that something very strange appears to be happening at the galaxy’s center. Above all, it’s a mystery, and a very juicy one; whether or not it’s a supermassive black hole binary on the verge of colliding, J1430+2303 appears to merit closer, more detailed scrutiny.