A Pair of Supermassive Black Holes Could Be Fated to Collide Within 3 Years

One of the most eagerly anticipated events in contemporary astronomy may be present in the strange behaviour of a galaxy about a billion light-years away.

The SDSS J1430+2303 galaxy's light fluctuations strangely resemble two supermassive black holes with a total mass of about 200 million Suns that are on the verge of colliding with one another.

In cosmic terms, the concept of "imminent" frequently lasts for a whole lifetime. Fortunately, astronomers believe that during the next three years, if the signal is actually the consequence of massive black holes, they will merge.

Although J1429+2303 may be our best chance to date to witness the collision of two supermassive black holes, we are yet unsure of its precise nature. We should keep observing the peculiar galaxy, say scientists, to see if we can positively identify it.

In 2015, the first evidence of two black holes colliding was discovered, ushering in a brave new age in astronomy. Due to the gravitational waves that these enormous events cause to ripple through space-time, numerous more detections have been made since that time.

 

Almost all of these mergers to yet have included binary pairs of black holes, each of which has a mass around that of a single star. There is a strong rationale behind this. The gravitational wave detectors LIGO and Virgo, which made the detections, are made for masses in this range.

For our existing observatories, the frequency range is too low to detect the more ponderous ripples produced by inspiralling and colliding supermassive black holes, which are millions to billions of times more massive than the Sun.

 

Still, it would be really delightful to witness two supermassive black holes combine. Scientists anticipate a massive outpouring of light across the spectrum, even in the absence of a detector that can detect low frequency gravitational waves.

We may learn a great deal about how these events unfold from the information included in that outburst. Although the exact mechanism behind supermassive black hole growth is unknown, there are some indications that binary mergers may be one of the possible causes.

Supermassive black holes are known to exist in the cores of galaxies, and we have seen that at the centres of these post-merger galaxies, in addition to pairs and groups of galaxies colliding, supermassive black holes are also revolving around one another in mutual, decaying orbits. These are deduced from oscillations in the light these galaxies emanate from their galactic centres, which occur on predictable timeframes and seem to indicate an orbit.

This brings up J1430+2303 once more. The University of Science and Technology of China's Ning Jiang headed a group of astronomers who earlier this year published a document to the public server arXiv revealing some really peculiar behaviour. The galactic nucleus oscillations shrunk from a time interval of nearly a year to just one month during the course of three years.

However, it's not entirely clear that what is happening at the heart of J1430+2303 is the result of a black hole binary at all, never mind one that is about to kaboom. Galactic nuclei are strange places, throwing out signals that are difficult to interpret, meaning it's possible something else may be causing the variability in the heart of J1430+2303.

 

Astronomers used X-ray wavelengths to attempt and understand the issue. A team lead by Liming Dou of Guangzhou University in China has made an effort to find high-energy signs that we would expect to detect in a local supermassive black hole binary on a decaying orbit using data from a variety of X-ray observatories covering a time period of 200 days.

The scientists did observe fluctuations in the galaxy's X-ray brightness as well as a specific form of emission linked to iron colliding with a black hole, which they were able to detect with a 99.96% confidence level from two independent equipment. The scientists could not measure the "smoking gun" characteristics that would confirm a black hole binary, although this emission can be linked to binary supermassive black holes.

Additionally, an analysis of radio data published in July came up empty. Therefore, it seems that we are still unsure of exactly what is going on with J1430+2303.

We can say with certainty that something incredibly unusual appears to be happening at the galaxy's centre. Above all, it's a mystery, and a pretty juicy one at that; J1430+2303 seems to demand closer, more in-depth consideration whether or not it's a supermassive black hole binary on the verge of collision.

The paper has been accepted for publication in Astronomy & Astrophysics, and is available on arXiv.