Artist’s impression: Supermassive black holes at the heart of every galaxy slam into each other, sending gravitational shock waves through the universe
Scientists have captured shock waves from the orbit of supermassive black holes at the heart of distant galaxies as they begin to merge.
This may be the first direct evidence of giant black holes warping space and time as they roll in on each other.
The theory is that this is how galaxies grow. Now, astronomers may soon be able to watch this happen.
These distortions happen all the time, throughout the universe.
One of the groups that made the discovery is the European Pulsar Timing Consortium (EPTA), led by Prof. Michael Kramer of the Max Planck Institute for Radio Astronomy in Bonn.
He told BBC News that the discovery has the potential to change astronomers’ understanding of space forever.
“This could tell us whether Einstein’s theory of gravity was wrong; it can tell us what dark matter and dark energy, the mysterious stuff that makes up most of the universe, really are, and it can give us a new window into new theories of physics.”
A real picture of the supermassive black hole at the heart of our own galaxy
Further study may provide new insights into the role that supermassive black holes play in the evolution of all galaxies.
Dr Rebecca Bowler of the University of Manchester told BBC News that researchers believe there are giant black holes at the heart of all galaxies and that they grow over billions of years. But so far this has all been theoretical.
“We know supermassive black holes exist, but we don’t know how they got there. One possibility is that the smaller black holes are merging, but there is little observational evidence for this.
“But with these new observations, we could see such a merger for the first time. And that will directly tell us how the most massive black holes form,” she said.
The observations were made by studying signals from dead stars called pulsars. They rotate and send out bursts of radio signals at extremely precise intervals.
But researchers, who include astronomers from the Lovell Telescope at Jodrell Bank in Cheshire and from the University of Birmingham, have found that these signals reach Earth slightly faster or slower than they should. And they say the time warp is consistent with gravitational waves created by merging supermassive black holes in the universe.
The Lovell Giant Antenna was among the telescopes used to detect the shock waves
Dr Stanislav Babak of Laboratory APC at CNRS, France, said gravitational waves carry information about “some of the best-kept secrets of the universe”.
The newly discovered gravitational waves are different from those detected before. These earlier waves are caused by much smaller star-sized black holes crashing into each other.
The type described in the latest research is believed to be black holes that are hundreds of millions of times more massive, spiraling towards each other as they get closer.
Their gravitational pull is so powerful that it warps time and space, a process that can take billions of years until the supermassive black holes finally merge.
The gravitational waves that scientists detected earlier can be thought of as short rumbles, while the new ones are similar to the background hum that is around us all the time.
Their next step is to take more readings and combine the observations. With further progress, another goal is to be able to detect individual pairs of supermassive black holes – assuming they are the source.
Gravitational waves may also be caused by other exciting phenomena, such as the first ever black holes or exotic structures called cosmic strings, both of which can be thought of as the seeds from which the universe grew.
What are gravitational waves?
Gravity is a constant force in our daily lives. If you drop a cup, it falls and smashes on the ground every time you do. But in space, gravity doesn’t stay the same. It can change if there is a sudden and catastrophic event – such as a collision of black holes.
The event is so cataclysmic that space and time itself are warped and ripples are sent through the universe – as happens when a pebble is dropped into a lake.
In the case of gravitational waves, everything in the universe—the stars, the planets, and even us—is water. Everything is compressed and stretched and then crushed and flattened ever so slightly as the waves pass over us. And just like in a pond, the ripples quickly diminish and disappear.
Gravitational waves from merging star-sized black holes were directly detected for the first time in 2015. Very sensitive laser systems measured the waves produced in the final moments before the collision.
For the type of waves coming from inspiring supermassive black holes, the pulsar approach captures the waves produced in the billions of years before the final merger.
It is similar to a continuous stream of pebbles thrown into the lake. And since the mergers are happening all over the cosmos, the signal looks like a cacophony.
EPTA combined the results with a consortium in India (InPTA) and published the results of their research in the journal Astronomy and Astrophysics.
Three other separate, competing research groups from North America (NANOGrav), Australia (PPTA) and China (CPTA) published similar estimates, causing a great stir in the physics and astronomy community.
Scientists must first confirm their observations. None of the research groups had data that met the gold standard of less than a one-in-a-million chance of error, which is usually required for convincing evidence—though combined, the results of the different teams are certainly compelling.