According to Einstein's general theory of relativity and also, most astronomers believe that black holes are cosmic singularities with no physical surface area, surrounded by an invisible gravitational barrier known as the event horizon.
While the supermassive black holes are thought to exist at the heart of almost all galaxies, including our own, there is another opinion based on modified theories of general relativity, suggest that instead of a black hole there is a central massive object that has somehow managed to avoid gravitational collapse to a singularity and have hard surface area.
When a star hits a black hole.
So, what happens when a star falls into a supermassive black hole? Does it swallowed entirely by the black hole or crash into the hard surface of a massive object and get destroyed.
Pawan Kumar an astrophysicist from the University of Texas at Austin along with his team, come up with a test to determine which theory is correct. "Our whole point here is to turn this idea of an event horizon into an experimental science, and find out if event horizons really do exist or not," said Pawan Kumar.
The researchers tried to figure out what would be the scenario if a star hit the hard surface of a supermassive object at the center of a galaxy, the star’s gas would envelope the object, shining visibly for months or perhaps even years. Once they knew what to search for, the team calculated how often this should be seen in the nearby galaxies.
Then they searched a recent archive of telescope observations made by Pan-STARRS telescope in Hawaii. During a period of 3.5 years, the telescope scanned half of the northern hemisphere sky, looking for 'transients', things that glow for a while and then fade.
Their aim was to find transients with the expected light signature of a star falling toward a supermassive object and hitting a hard surface. "Given the rate of stars falling onto black holes and the number density of black holes in the nearby universe, we calculated how many such transients Pan-STARRS should have detected over a period of operation of 3.5 years. It turns out it should have detected more than 10 of them if the hard-surface theory is true," explains one of the team, Wenbin Lu.
So, did they find any?
No, they did not find any transients with that expected light signature of a star hitting a supermassive object. It means that when a star falls into a supermassive black hole, it just simply pass the event horizon and vanishes completely.
"Our work implies that some, and perhaps all, black holes have event horizons and that material really does disappear from the observable universe when pulled into these exotic objects, as we've expected for decades. General Relativity has passed another critical test," says one of the researchers, Ramesh Narayan from the Harvard-Smithsonian Center for Astrophysics.
The researchers are now proposing to improve the test with a larger telescope, the Large Synoptic Survey Telescope, presently under construction in Chile. LSST will perform surveys like the Pan-STARRS telescope, but with much greater sensitivity.
Image Credit: NASA/JPL-Caltech
Source: University of Texas
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