Paris: First postulated more than 230 years ago, black holes have been extensively researched, frequently depicted, even featured in sci-fi films.
We’ve all seen the artists’ impressions and read of their ravenous star-gobbling feasts.
But here’s the thing ... science is still not 100 per cent sure what they look like, how they behave or even that they exist.
This photo shows deep in the heart of the Abell 2597 Brightest Cluster Galaxy, a small cluster of giant gas clouds raining in on what is believed to be the central black hole. - AFP
Telescopes have never seen a black hole, and the world’s brightest minds are unable to reconcile their core characteristics with some of the bedrock laws of nature.
Seeking answers, scientists have trained a massive telescope, named Gravity, in Chile on a point some 24,000 light years away where a supermassive black hole is thought to lurk at the centre of our Milky Way galaxy.
The enormous eye will look for minuscule but telltale deviations in the movement of gas and stars swirling around the monster hole.
“The goal of Gravity is to finally prove the existence of a black hole at the centre of our galaxy,” project member Guy Perrin, an astronomer from the Paris Observatory, told AFP.
But finding something unexpected would in some ways be an even bigger breakthrough as it may offer clues to our imperfect understanding of physics.
Gravity’s theorised target, Sagittarius A, is four million times more massive than our Sun, packed into an area smaller than the Solar System.
To observe it up close, astronomers have combined the power of Europe’s four largest telescopes, based in the Atacama Desert, to create the most powerful instrument of its kind ever built.
The images will be “about 10-20 times sharper than what we had before,” said project leader Frank Eisenhauer of the Max Planck Institute for Extraterrestrial Physics.
With a combined diameter of about 130 metres, the device will allow astronomers to observe more detail, closer to the black hole, than ever before.
“We will check whether our physical understanding is correct to conclude it is a black hole,” Eisenhauer told AFP by telephone from Atacama, where the telescope is being put through its paces before starting full-scale observations, probably next year.
“If you see the motion of matter so close to a black hole, it would be very difficult to find any other explanation.”
Black holes are regions in space-time where mass is collapsed into such a small area that gravity takes over completely, and nothing can escape its pull.
Eighteenth century amateur clergyman and scientist John Michell is credited with conceptualising black holes in 1783.
They were also predicted in Albert Einstein’s theory of general relativity, published in 1915.
There are two types: “stellar mass” black holes that form when a monster star implodes, and the “supermassive” variety which lie at the centre of large galaxies.
Ubiquitous as they are believed to be — millions in the Milky Way galaxy alone — black holes are invisible because they absorb light, along with everything else.
Their existence is inferred from the behaviour of objects nearby, including stars swirling around them as planets orbit our Sun.
Some scientists, including physicist Stephen Hawking, have suggested black holes — if they exist at all — may not fit the general relativity mould.
In February, evidence for stellar mass black holes emerged when scientists observed a gravitational wave — a ripple theorised to move through space-time when two of these beasts collide.
Each black hole, in Einstein’s world, should have an “event horizon,” a point of no return beyond which gravity takes over.
But a major problem in science today is that general relativity does not gel with quantum mechanics, the other pillar of modern physics.
Quantum physics perfectly describes phenomena on the minuscule, subatomic level, but gravity does not seem to work on that scale.
When it comes to black holes, general relativity predicts that nothing can escape them. Quantum theory, however, posits that no information from the Universe can ever just disappear.
By zooming in so close on the event horizon, “we will be able to test a number of theories in an environment with an extreme gravitational field,” said Karine Perraut of the Grenoble Observatory in southeast France.
It will be the toughest test yet for general relativity, which has withstood all other science challenges.
For Einstein to be right, the Gravity team would have to see the stars’ orbit change slightly with every full rotation around the black hole.
But what it would look like if Einstein was wrong, nobody knows.
“I can only imagine the shock if we cannot confirm that it is a black hole. It will have huge implications for our understanding of the Universe!” said Perrin.
Gravity started early operations in June and is expected to report on progress next week.
Second gravitational wave detected from ancient black hole collision
Physicists have detected ripples in the fabric of space-time that were set in motion by the collision of two black holes far across the universe more than a billion years ago.
The event marks only the second time that scientists have spotted gravitational waves, the tenuous stretching and squeezing of space-time predicted by Einstein more a century ago.
The faint signal received by the twin instruments of the Laser Interferometer Gravitational Wave Observatory (LIGO) in the US revealed two black holes circling one another 27 times before finally smashing together at half the speed of light.
The cataclysmic event saw the black holes, one eight times more massive than the sun, the other 14 times more massive, merge into one about 21 times heavier than the sun. In the process, energy equivalent to the mass of the sun radiated into space as gravitational waves.
“This is confirmation that there’s a real population of black holes out there waiting to be detected in the future,” said John Veitch, an astrophysicist on the LIGO team at the University of Birmingham.
In February, researchers on the instrument made the historic announcement that they had picked up gravitational waves for the first time. The twin pieces of equipment, one in Hanford, Washington state, the other in Livingston, Louisiana, recorded the ripples in September 2015 as minuscule distortions in laser beams sent down 4km-long tubes. The detectors are so sensitive they can pick up changes in length one thousandth the diameter of a proton.
Writing in the journal Physical Review Letters on Wednesday, the LIGO team describes how a second rush of gravitational waves showed up in their instrument a few months after the first, at 3.38am UK time on Boxing Day morning 2015. An automatic search detected the signals and emailed the LIGO scientists within minutes to alert them.
The latest signals arrived at the Livingston detector 1.1 milliseconds before they hit the Hanford detector, allowing scientists on the team to roughly work out the position of the collision in the sky. At least one of the black holes was spinning.
Closed for upgrade work in January this year, LIGO is expected to switch back on in the autumn with improvements that will nearly double the amount of the universe it can observe.
According to Will Farr, another LIGO researcher at Birmingham, pairs of black holes slam into one another on average once every 15 minutes in the observable universe.
“For me, the first detection broke everything wide open, but there was always the possibility that we had got phenomenally lucky. With the second signal it’s clear we are starting to see a population. We are going to see many of more of these in the next run,” he said.
— Guardian News & Media Ltd.