October 18th, 2011
Econintersect: Astrophysicists have long sought evidence that black holes swallowed stars. These centers of matter so densely concentrated that the internal gravity will allow nothing entering to escape, not even light. Black holes are thought to be formed when massive stars end their life in a supernova which then collapses into a dense mass. New research has found observations from data collected from over 2,000 galaxies indicating that stars can be destroyed by black holes even when they are not completely captured. A black hole can actually pull a star apart. Follow up:
Follow up:Wikipedia has the following description of a black hole:
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that marks the point of no return. It is called "black" because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body in thermodynamics. Quantum mechanics predicts that black holes emit radiation like a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of stellar mass or greater.
Objects whose gravity field is too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916, although its interpretation as a region of space from which nothing can escape was not fully appreciated for another four decades. Long considered a mathematical curiosity, it was during the 1960s that theoretical work showed black holes were a generic prediction of general relativity. The discovery of neutron stars sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality.
An article in Scientific Computing describes how a new interaction of stars with black holes has been discovered. The discovery involves an event called a TDF (tidal disruption flare) which occurs when a star is shredded by a nearby black hole and some of the star matter not captured by the black hole collides upon itself creating intense radiation. The TDFs are very difficult to identify because they are outnumbered by supernovae by 1000 to 1.
From Scientific Computing:
The researchers on the Astrophysical Journal study uncovered sound evidence for the presence of two TDFs through a rigorous analysis of archival data from the Sloan Digital Sky Survey, or SDSS.
To do so, they sifted through voluminous SDSS data in which more than 2 million galaxies were repeatedly observed over 10 years. By very carefully registering the images and looking at differences between consecutive images, they obtained a sample of 342 intense and well-measured flares.
Of these, almost all could be classified into supernovae and AGN flares. However, two cases were left that did not fit either classification. By relying on multi-year observations, the researchers could see that the two flares' host galaxies showed no other flaring activity, as would be the case if the flares came from a hidden variable AGN. This means the possibility these two flares were produced by undetected AGNs is extremely small.
In addition, the researchers located these flares at the nucleus of their galaxy with high precision, which reduces the likelihood that they are supernovae to less than 1 percent since supernovae are randomly distributed through galaxies.
Finally, the properties of these flares are very different from flares of AGNs and supernovae -- and their spectra are unlike any supernovae observed to date. Supernovae flares are characteristically very blue at first but become red as they cool and rapidly decay, whereas the TDF flares are very blue throughout -- slowly decaying without changing color.
AGN stands for Active Galactic Nuclei which are created by accreting material emitting light as it swirls around a black hole before being finally pulled in. A more common name for an AGN is “quasar”.