BLACKHOLES

Lindy Lou YamiloCyren Andit

Rochel AgbayaniEarl Jan Tampus

III-Galileo

A Black hole is a hypothetical body with a gravitational field so strong that nothing, including electromagnetic radiation, can escape from its vicinity. The body is surrounded by a spherical boundary, called a horizon, through which light can enter but not escape; it therefore appears totally black, hence the name.

Such a field can belong to a high-density body, of relatively small mass, less than or equal to that of the sum, compressed into a very small volume; or to a low-density body of very great mass, such as a collection of millions of stars at a galaxy's center.

CONCEPTUALIZINGBLACK HOLES

The Black hole concept was developed by the German astronomer Karl Schwarzschild in 1916, on the basis of Albert Einstein's “Theory of General Relativity”. The radius of the horizon of a Schwarzschild black hole depends only on the mass of the body: in kilometers it is 2.95 times the mass of the body in solar units - that is, the mass of the body divided by the mass of the Sun. If the body is electrically charged or rotating, Schwarzschild's result are modified. An “ergosphere” forms outside the horizon, within which matter is forced to rotate with the black hole; in principle, energy can be emitted from the ergosphere.

According to general relativity, gravitation severely modifies space and time near a black hole. As the horizon is approached from outside, time slows down relative to that of the distant observers, stopping completely on the horizons. Once the body has contracted within its Schwarzschild radius, it would theoretically collapse to a singularity, that is a dimensionless object of infinite density.

EVIDENCE OFBLACK HOLES

Astronomers have discovered X-ray emissions from a binary system, Cygnus X-1, in which the primary is a normal star of about 30 solar masses. Doppler shifts in its spectrum show that a companion object of 10 to 15 solar masses must be in orbit around it; evidence exists that the X-rays originate near the companion. Normally such X-rays are produced by an “accretion disc”, a dense, hot disc of gas that forms as the gas from a normal star spirals into a compact object.

Astronomers have discovered X-ray emissions from a binary system, Cygnus X-1, in which the primary is a normal star of about 30 solar masses. Doppler shifts in its spectrum show that a companion object of 10 to 15 solar masses must be in orbit around it; evidence exists that the X-rays originate near the companion. Normally such X-rays are produced by an “accretion disc”, a dense, hot disc of gas that forms as the gas from a normal star spirals into a compact object.

The companion in Cygnus X-1, because of its massiveness, is thought likely to be a black hole rather than a white dwarf or neutron star. Other potential candidates for a black hole are an X-ray source in a galaxy neighboring our own, the Large Magellanic Cloud, and another X-ray source located in the constellation Monoceros. Astrophysicist conjecture that many, if not all, galaxies of substantial size may contain black holes at their centers.

In 1994 the Hubble Space Telescope provided strong evidence that a black hole exists at the center of the galaxy M87. The high acceleration of gases in this region indicates that an object, or group of objects, of 2.5 billion to 3.5 billion solar masses must be present.

The english physicist Stephen Hawking has suggested that many black holes may have formed in the early universe. If this is so, many of these black holes could be too far from other matter to form detectable accretion disc, and they could even compose a significant fraction of the total mass of the universe. In reaction to the concept of singularities. Hawking has also proposed that black holes do not collapse in this manner but instead form “wormholes” to other universes beside our own.

A black hole of sufficiently small mass can capture one member of an electron-positron pair near the horizon, the other escaping. The resulting radiation carries off energy, in a sense evaporating the black hole. Any primordial black hole weighing less than a few billion tons would already have evaporated, but heavier ones may remain.

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