Monday, August 15, 2022

For the first time, a black hole was discovered outside our galaxy using an ingenious method

Black holes are masters of cunning.

If they do not absorb material more actively than most stellar mass black holes, they do not emit radiation that we can detect. Therefore, we must resort to other means of detecting them – for example, looking for stars that appear to be in a double orbit without … nothing.

Now astronomers have been able to find a black hole outside the Milky Way galaxy for the first time using this method.

From the motion of a spinning star, they identified a relatively small black hole in the Large Magellanic Cloud, a dwarf galaxy orbiting the Milky Way about 160,000 light-years away.

The black hole, dubbed NGC 1850 BH1, was discovered, you guessed it, in NGC 1850, a cluster of thousands of stars. The discovery suggests that this method may indeed be the key to finding black holes in densely populated star clusters, in the Milky Way and beyond.

“Like Sherlock Holmes tracking down a criminal gang for its mistakes, we look at every star in this cluster with a magnifying glass in one hand, trying to find evidence of the presence of black holes, but not directly observing them,” says astrophysicist Sarah Saracino of the University of Liverpool John Moore in the UK.

“The result shown here represents only one of the wanted criminals, but when you find it, you’re on your way to finding many more in different groups.”

Most of the black holes we have discovered outside the Milky Way have given themselves away from radiation that erupts when they are active. The black hole itself does not emit radiation, but the material falling on it emits – in fact, a lot of radiation.

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Since 2015, we’ve also discovered a growing number of black holes due to gravitational waves, the smallest waves they generate in spacetime when two objects collide. However, despite all these advances, it is still a drop in the cosmic ocean.

Astronomers have calculated that the Milky Way alone could have 100 million stellar mass black holes. We did not even find that many objects, which means that there are quite significant gaps in our understanding of these mysterious objects.

However, the way objects about The behavior of black holes can be a sure sign of their presence. Although they may be physically small and dark (a black hole 11 times the mass of the Sun would have an event horizon only 65 kilometers or 40 miles across), they still exert a gravitational effect on the space around them.

For example, when a black hole captures a star in a double orbit, that star begins to move in a characteristic manner. Although from the distance at which we observe, it may appear that it is standing still, its light will change: the wavelength will increase as the star moves away from us and contract as it moves towards us.

“Overwhelming majority [of black holes] open only dynamically, ”says astronomer Stefan Dreizler of the University of Göttingen in Germany.

“When they form a system with a star, they will affect its movement in a subtle but noticeable way, so we can find them with sophisticated tools.”

Sarachino and her team collected data over two years using the Very Large Telescope’s Multi Unit Spectroscopic Explorer (MUSE) and then analyzed the data looking for wavelength changes that indicate a binary star, excluding any system with a visible satellite.

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The result of all this painstaking work was the discovery of NGC 1850 BH1. Its companion star is about 5 times the mass of the Sun and is at the very end of its life on the main sequence. It’s very close to the black hole, with an orbital period of only 5 days – so close that when the star inflates and begins to die, material will likely begin pumping into the black hole.

But there is another reason the discovery is so exciting. The star cluster NGC 1850 is very young from a cosmic point of view – it is only 100 million years old. NGC 1850 BH1 represents the potential for finding even younger black holes, which in turn could help us understand how these objects form and develop.

Finding black holes in young star clusters can help us understand the evolutionary stages between a massive star and a neutron star or black hole, as well as statistics on the population of black holes in star clusters. Since astronomers believe that collisions between black holes and neutron stars are most likely in star clusters, this also has implications for the field of gravitational wave astronomy itself.

“Each of our discoveries will be essential to our future understanding of star clusters and black holes in them,” said astronomer Mark Giles of the University of Barcelona in Spain.

Research published in Royal Astronomical Society Monthly Notices

Nation World News Desk
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