Colossal black holes locked in dance at heart of galaxy

There are two black holes that are 9 billion light years away, and they are circling each other every two years. The two giant bodies are hundreds of millions of times larger than the sun, and they are separated by 50 times. The titanic collision is expected to shake space and time and cause ripples in the universe.

Evidence for this scenario has been found by a Caltech-led team of astronomer. A quasar is an active core of a galaxies in which a black hole sucks material from a disk. In some quasars, a black hole creates a jet that shoots out at high speeds. The quasar observed in the new study is a blazar, a subclass of quasars in which the jet is pointing toward the Earth. Astronomers knew that quasars could have two black holes, but it has been difficult to prove it.

The researchers argue in The Astrophysical Journal Letters that the second candidate for a pair of black holes caught in the act of merging is the same one as the first. The first candidate pair, within a quasar called OJ 287, will circle each other at greater distances for nine years, compared to two years for the second candidate pair.

The evidence came from radio observations for 45 years. According to the study, a powerful jet from one of the black holes within PKS is shifting back and forth due to the pair's motion. Changes in the radio-light brightness are caused by this. Caltech's Owens Valley Radio Observatory (OVRO), the University of Michigan Radio Astronomy Observatory (UMRAO), MIT's Haystack Observatory, and the National Radio Astronomy Observatory were all registered.

The combination of the radio data yields a perfect light curve.

When we realized that the peaks and troughs of the light curve detected from recent times matched the peaks and troughs observed between 1975 and 1983, we knew something very special was going on.

There are ripples in space and time.

Our own Milky Way galaxy has a black hole at its core. When the black holes in the middle of the newly formed galaxy sink to the center of the other black holes, they form an even larger black hole. Albert Einstein predicted 100 years ago that black holes would cause ripples in the fabric of time and space.

Caltech and MIT manage the National Science Foundation's LIGO, which can detect waves from black holes up to the mass of our sun. The black holes at the center of the galaxies have mass that is ten times that of the sun and give off less waves than LIGO.

In the future, the pulsar timing array should be able to detect the waves from black holes. The Laser Interferometer Space Antenna, or LISA, would detect merging black holes whose mass is 10 million times greater than the mass of our sun. The most promising target has yet to be registered from any of these heavier sources.

Light waves are the best way to detect black holes.

The first candidate, OJ, has periodic radio-light variations. The black holes tend to circle each other every nine years, but these fluctuations are more irregular. The black holes within the new quasar are about 50 times larger than the sun and 100 times larger than the pair in OJ 287. The distance between Earth and the sun is an astronomy unit.

The light curve is revealed.

Readhead says the discoveries unfolded like a good detective novel, beginning in 2008 when he and colleagues began using the 40-meter telescope at OVRO to study how black holes convert material into jets. They noticed a unique case in 2020 when they were monitoring the brightness of more than 1,000 blazars.

Readhead says that there is a pattern that can be traced continuously over time.

The research team looked for peaks in the light curves that matched predictions based on the more recent OVRO observations. There was a peak from 2005 that matched predictions. The UMRAO data shows there was no signal for 20 years before 1981 when another peak was observed.

The story would have stopped as we didn't know there was data before 1980. This beautiful finding would be sitting on the shelf if it weren't for her.

As part of Caltech's Summer Undergraduate Research Fellowship program, O' Connell began working with Readhead and the study's second author Sebastian Kiehlmann. The astronomy project was the one that O'Neill picked up because she wanted to stay active during the Pandemic.

The Haystack Observatory had made radio observations of the object between 1975 and 1983 when the project was back on the table. The peak that was revealed was in 1976, matching their predictions.

The work shows the value of doing accurate monitoring of these sources over many years for performing discovery science, says co-author Roger Blandford.

Like clockwork.

The system of the jet moving back and forth is compared to a clock, where each cycle corresponds to the two years of the black holes, because light is stretched by the expansion of the universe. The black hole's fueling caused this tick to disappear for 20 years after it was first seen in 1976. The tick has been there for 17 years.

The stability of the period over this 20-year gap strongly suggests that this blazar harbors not one supermassive black hole, but two supermassive black holes.

Blandford came up with an elegant model to explain the physics behind the variations.

Readhead says that they knew that the beautiful sine wave had to be telling something about the system. Before Roger worked it out, nobody had figured out that the light curve looked like this.

Kiehlmann says their study provides a plan for how to search for blazar binaries in the future.

More information: S. O'Neill et al, The Unanticipated Phenomenology of the Blazar PKS 2131–021: A Unique Supermassive Black Hole Binary Candidate, The Astrophysical Journal Letters (2022). DOI: 10.3847/2041-8213/ac504b Journal information: Astrophysical Journal Letters Citation: Colossal black holes locked in dance at heart of galaxy (2022, February 23) retrieved 23 February 2022 from https://phys.org/news/2022-02-colossal-black-holes-heart-galaxy.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.