Cosmos Editorial
We still don’t understand a lot about black holes – objects that are so massive and sense that nothing can escape their gravitational pull, not even light. Inside a black hole, our understanding of the laws of physics breaks down, making them one of the most tantalising cosmic mysteries.
But this year saw a surge of awesome black hole research, from gravitational wave detections to mapping magnetic fields to searches for dark matter swirling around them.
Let’s take a look at the highlights.
1. Black hole gulps down neutron star
For the first time, scientists detected gravitational waves from a black hole swallowing a neutron star – and not just once, but twice.
Previous detections had captured these captured ripples in space-time reverberating out from cataclysmic collisions between two black holes and two neutron stars.
But now, scientists have finally completed the trifecta by spotting the death spiral of a neutron star into a black hole – an awesome milestone for the field of gravitational-wave astronomy.
2. Could black holes power alien civilisations?
Scientists reckon that building energy-harvesting structures around black holes could be effective to power massive alien civilisations.
If an alien society’s energy needs outstripped the supply of its planet, physicists have theorised that it could build a megastructure known as a ‘Dyson sphere’ around its host star to harness the power on a massive scale.
That means we could spot alien civilisations by looking for these structures.
This year, Taiwanese researchers crunched the numbers and found that a Dyson sphere could work around a black hole, too – and they even calculated whether we’d be able to see it.
3. First light detected from behind a black hole
Astrophysicists have caught sight of light reflected from behind a black hole, proving Einstein right yet again.
You may have heard that nothing – not even light – can escape a black hole, but this isn’t strictly true. Anything that crosses the event horizon is forever lost, but the hot disc of matter swirling around the black hole can emit dazzlingly powerful X-rays visible from Earth.
However, not all of this light escapes easily.
A new study found ‘flashes’ of X-rays different to the normal, more luminous emissions – and they seemed to be reflected from behind the black hole.
4. How big is a black hole? Watch how it eats
The feeding patterns of a black hole can tell us about its size, say researchers in the journal Science.
When actively consuming matter, supermassive black holes release dazzling bursts of radiation-like burps, in flickering patterns that vary over timescales from hours to decades.
Researchers have long wondered whether the timing of these patterns could tell us more about the black hole itself.
Turns out, they can: the more massive a black hole is, the longer it takes between ‘burps’ of light.
5. Magnetic fields mapped around black hole
The Event Horizon Telescope (EHT) snapped a new image of the massive object lurking at the centre of the Messier 87 (M87) galaxy – this time, in polarised light.
Astronomers think this is exciting stuff, because it’s the first time that polarisation – a signature of magnetic fields – has been measured so close to the edge of a black hole.
“We are now seeing the next crucial piece of evidence to understand how magnetic fields behave around black holes, and how activity in this very compact region of space can drive powerful jets that extend far beyond the galaxy,” says Monika Mościbrodzka, co-author of the new research from Radboud University in the Netherlands.
6. Could gravitational waves help us find dark matter?
Astronomers have used super-sensitive gravitational wave instruments to look for boson clouds, a leading contender for dark matter – in the swirling discs around black holes.
These clouds are of subatomic particles called ultralight bosons, predicted by theories that reach beyond the standard model of particle physics.
These bosons are almost impossible to detect on Earth, but astronomers think they may exist around black holes and send out specific gravitational wave signals – so they used LIGO to look for them.
7. More gravitational waves detected than ever before
An international team of researchers has made a whopping 90 detections – the largest number of gravitational wave detections to date.
Of the 35 detections in this latest observing round, 32 were caused by two black holes merging. Two were likely caused by a neutron star – a dense, city-sized star that’s heavier than our own Sun – smashing into a black hole.
And one had mysterious origins.
8. Black holes belch out intergalactic smoke
Astronomers watched the evolution of streamers of gas around an active black hole – and they look a bit like the smoke produced by a volcanic eruption.
The team studied a system of 20 galaxies called Nest200047, 200 million light-years away. One of these galaxies has an active black hole at its heart, which produces radio jets that in turn create bubbles and other structures in the surrounding gas.
9. Black holes exert ‘quantum pressure’ on their environment
Black holes aren’t as single-minded as we thought. It turns out their quantum behaviour adds a new, recalcitrant dimension to their monstrous character.
In a first-of-its-kind discovery, UK physicists have found that black holes exert quantum pressure on their environment.