Do Stars Fall Into Black Holes, or Crash Into Something Unknown?

The first in a sequence of two artist's impressions that shows a huge, massive sphere in the center of a galaxy, rather than a super-massive black hole. Here a star moves toward and then smashes into the hard surface of the sphere, flinging out debris. The impact heats up the site of the collision. (Image:
  Mark A. Garlick/CfA)
The first in a sequence of two artist's impressions that shows a huge, massive sphere in the center of a galaxy, rather than a super-massive black hole. Here a star moves toward and then smashes into the hard surface of the sphere, flinging out debris. The impact heats up the site of the collision. (Image: Mark A. Garlick/CfA)

AUSTIN, Texas — Astronomers at the University of Texas at Austin and Harvard University have put a basic principle of black holes to the test, showing that matter completely vanishes when pulled in. Their results constitute another successful test for Albert Einstein’s General Theory of Relativity.

Most scientists agree that black holes, cosmic entities of such great gravity that nothing can escape their grip, are surrounded by a so-called event horizon. Once matter or energy gets close enough to the black hole, it cannot escape — it will be pulled in. Though widely believed, the existence of event horizons has not been proved. Pawan Kumar, a professor of astrophysics at The University of Texas at Austin, said:

Supermassive black holes are thought to lie at the heart of almost all galaxies. But some theorists suggest that there’s something else there instead — not a black hole, but an even stranger supermassive object that has somehow managed to avoid gravitational collapse to a singularity surrounded by an event horizon.

The first in a sequence of two artist's impressions that shows a huge, massive sphere in the center of a galaxy, rather than a supermassive black hole. Here a star moves towards and then smashes into the hard surface of the sphere, flinging out debris. The impact heats up the site of the collision. (Image: via Mark A. Garlick/CfA)

The first in a sequence of two artist’s impressions that shows a huge, massive sphere in the center of a galaxy, rather than a super-massive black hole. Here, a star moves toward and then smashes into the hard surface of the sphere, flinging out debris. The impact heats up the site of the collision. (Image: Mark A. Garlick/CfA)

The idea is based on modified theories of General Relativity, Einstein’s theory of gravity. While a singularity has no surface area, the noncollapsed object would have a hard surface. So material being pulled closer — a star, for instance — would not actually fall into a black hole, but hit this hard surface and be destroyed.

Kumar, his graduate student Wenbin Lu, and Ramesh Narayan, a theorist from the Harvard-Smithsonian Center for Astrophysics, have come up with a test to determine which idea is correct,

The team figured out what a telescope would see when a star hit the hard surface of a super-massive object at the center of a nearby galaxy: The star’s gas would envelope the object, shining for months, perhaps even years. Once they knew what to look for, the team figured out how often this should be seen in the nearby universe, if the hard-surface theory is true. Lu said:

They then searched a recent archive of telescope observations. Pan-STARRS, a 1.8-meter telescope in Hawaii, recently completed a project to survey half of the northern hemisphere sky. The telescope scanned the area repeatedly during a period of 3.5 years, looking for “transients” — things that glow for a while and then fade.

In this second artist's impression a huge sphere in the center of a galaxy is shown after a star has collided with it. Enormous amounts of heat and a dramatic increase in the brightness of the sphere are generated by this event. The lack of observation of such flares from the center of galaxies means that this hypothetical scenario is almost completely ruled out. (Image: via Mark A. Garlick/CfA)

In this second artist’s impression, a huge sphere in the center of a galaxy is shown after a star has collided with it. Enormous amounts of heat and a dramatic increase in the brightness of the sphere are generated by this event. The lack of observation of such flares from the center of galaxies means that this hypothetical scenario is almost completely ruled out. (Image: Mark A. Garlick/CfA)

Their goal was to find transients with the expected light signature of a star falling toward a supermassive object and hitting a hard surface, Lu explained:

They did not find any, Narayan said:

Now the team is proposing to improve the test with an even larger telescope: the 8.4-meter Large Synoptic Survey Telescope (LSST, now under construction in Chile). Like Pan-STARRS, LSST will make repeated surveys of the sky over time, revealing transients — but with much greater sensitivity.

Provided by: The University of Texas at Austin

[Note: Materials may be edited for content and length.]

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