Black holes Recent pictures and captions Source- space.about.com Hubble Space Telescope Provides Multiple Views of How to Feed a Black Hole The Hubble Space Telescope offers a stunning unprecedented close-up view of a turbulent firestorm of star birth along a nearly edge-on dust disk girdling Centaurus A, the nearest active galaxy to Earth. The picture at upper left shows the entire galaxy. The blue outline represents Hubble's field of view. The larger, central picture is Hubble's close-up view of the galaxy. Brilliant clusters of young blue stars lie along the edge of the dark dust lane. Outside the rift the sky is filled with the soft hazy glow of the galaxy's much older resident population of red giant and red dwarf stars. Hubble Space Telescope Uncovers Dust Disk around a Massive Black Hole Resembling a gigantic hubcap in space, a 3,700-light-year-wide dust disk encircles a 300-million- solar-mass black hole in the center of the elliptical galaxy NGC 7052. The disk, possibly a remnant of an ancient galaxy collision, will be swallowed up by the black hole in several billion years. The black-and-white image on the left, taken by a ground-based telescope, shows the complete galaxy. The Hubble picture on the right is a close-up view of the dust disk surrounding the black hole. Very Long Baseline Array Reveals Formation Region of Giant Cosmic Jet Near a Black Hole Astronomers have seen the exhaust products of black hole "engines": narrow beams of material traveling at nearly the speed of light. But they could only speculate where and how those beams were created. Now astronomers have gained their first glimpse at the mysterious region near a black hole at the heart of a distant galaxy where those columns of material are formed. Images of this phenomenon, taken by radio telescopes in Europe and the U.S., are the most detailed ever of the center of the galaxy M87, some 50 million light-years from Earth. More Info Lone Black Holes Discovered Adrift in the Galaxy Astronomers using the Hubble telescope and ground-based observatories have discovered the first examples of isolated, stellar-mass adrift among the stars in our Milky Way Galaxy. They detected two of these lonely, invisible objects indirectly by measuring how their extreme gravity bends the light of a more distant star behind them. All previously known "stellar" have been found orbiting normal stars. Astronomers determined the presence of those compact powerhouses by examining their effect on their companion star. These new results suggest that black holes are common and that many massive but normal stars may end their lives as black holes instead of neutron stars, the crushed cores of massive stars that end their lives in supernova explosions. The findings also suggest that stellar-mass do not require some sort of interaction in a double-star system to form but may be produced in the collapse of isolated, massive stars, as has long been proposed by stellar theorists. More Info A Cosmic Searchlight Streaming out from the center of the galaxy M87 like a cosmic searchlight is one of nature's most amazing phenomena, a black-ho le-powered jet of electrons and other sub-atomic particles traveling at nearly the speed of light. In this Hubble telescope image, the blue jet contrasts with the yellow glow from the combined light of billions of unseen stars and the yellow, point-like clusters of stars that make up this galaxy. Lying at the center of M87, the monstrous black hole has swallowed up matter equal to 2 billion times our Sun's mass. M87 is 50 million light-years from Earth. More Info Feasting Black Hole Blows Bubbles A monstrous black hole's rude table manners include blowing huge bubbles of hot gas into space. At least, that's the gustatory practice followed by the supermassive black hole residing in the hub of the nearby galaxy NGC 4438. These NASA Hubble Space Telescope images of the galaxy's central region clearly show one of the bubbles rising from a dark band of dust. The other bubble, emanating from below the dust band, is barely visible, appearing as dim red blobs in the close-up picture of the galaxy's hub (the colorful picture at right). The background image represents a wider view of the galaxy, with the central region defined by the white box. More Info Black Holes Shed Light on Galaxy Formation Astronomers are concluding that monstrous weren't simply born big but instead grew on a measured diet of gas and stars controlled by their host galaxies in the early formative years of the universe. These results, gleaned from a NASA Hubble Space Telescope census of more than 30 galaxies, are painting a broad picture of a galaxy's evolution and its long and intimate relationship with its central giant black hole. Though much more analysis remains, an initial look at Hubble evidence favors the idea that titanic did not precede a galaxy's birth but instead co-evolved with the galaxy by trapping a surprisingly exact percentage of the mass of the central hub of stars and gas in a galaxy. More Info Hubble Space Telescope Captures an Extraordinary and Powerful Active Galaxy The Hubble telescope has taken a snapshot of a nearby active galaxy known as Circinus. This active galaxy belongs to a class of mostly spiral galaxies called Seyferts, which have compact centers and are believed to contain massive . Seyfert galaxies are themselves part of a larger class of objects called Active Galactic Nuclei or AGN. AGN have the ability to remove gas from the centers of their galaxies by blowing it out into space at phenomenal speeds. Astronomers studying the Circinus galaxy are seeing evidence of a powerful AGN at its center. More Info 'Death Spiral' Around a Black Hole Yields Tantalizing Evidence of an Event Horizon The Hubble telescope may have, for the first time, provided direct evidence for the existence of black holes by observing how matter disappears when it falls beyond the "event horizon," the boundary between a black hole and the outside universe. Astronomers found their evidence by watching the fading and disappearance of pulses of ultraviolet light from clumps of hot gas swirling around a massive, compact object called Cygnus XR-1. This activity suggests that the hot gas fell into a black hole. More Info Ancient Black Hole Speeds Through Sun's Galactic Neighborhood, Devouring Companion Star Data from the Space Telescope Science Institute'sDigitized Sky Survey has played an important supporting role in helping radio and X-ray astronomers discover an ancient black hole speeding through the Sun's galactic neighborhood. The rogue black hole is devouring a small companion star as the pair travels in an eccentric orbit looping to the outer reaches of our Milky Way galaxy. It is believed that the black hole is the remnant of a massive star that lived out its brief life billions of years ago and later was gravitationally kicked from its home star cluster to wander the Galaxy with its companion. More Info Hubble Space Telescope Discovers Black Holes in Unexpected Places Medium-size actually do exist, according to the latest findings from NASA'sHubble Space Telescope, but scientists had to look in some unexpected places to find them. The previously undiscovered black holes provide an important link that sheds light on the way in which grow. Even more oddly, these new black holes were found in the cores of glittering, "beehive" swarms of stars called globular star clusters, which orbit our Milky Way and other galaxies. The black hole in globular cluster M15 [left] is 4,000 times more massive than our Sun. G1 [right], a much larger globular cluster, harbors a heftier black hole, about 20,000 times more massive than our Sun. What is a black hole? A black hole is a region of space that has so much mass concentrated in it that there is no way for a nearby object to escape its gravitational pull. Since our best theory of gravity at the moment is Einstein's general theory of relativity, we have to delve into some results of this theory to understand black holes in detail, but let's start of slow, by thinking about gravity under fairly simple circumstances. Suppose that you are standing on the surface of a planet. You throw a rock straight up into the air. Assuming you don't throw it too hard, it will rise for a while, but eventually the acceleration due to the planet's gravity will make it start to fall down again. If you threw the rock hard enough, though, you could make it escape the planet's gravity entirely. It would keep on rising forever. The speed with which you need to throw the rock in order that it just barely escapes the planet's gravity is called the "escape velocity." As you would expect, the escape velocity depends on the mass of the planet: if the planet is extremely massive, then its gravity is very strong, and the escape velocity is high. A lighter planet would have a smaller escape velocity. The escape velocity also depends on how far you are from the planet's center: the closer you are, the higher the escape velocity. The Earth's escape velocity is 11.2 kilometers per second (about 25,000 m.p.h.), while the Moon's is only 2.4 kilometers per second (about 5300 m.p.h.). Now imagine an object with such an enormous concentration of mass in such a small radius that its escape velocity was greater than the velocity of light. Then, since nothing can go faster than light, nothing can escape the object's gravitational field. Even a beam of light would be pulled back by gravity and would be unable to escape. The idea of a mass concentration so dense that even light would be trapped goes all the way back to Laplace in the 18th century. Almost immediately after Einstein developed general relativity, Karl Schwarzschild discovered a mathematical solution to the equations of the theory that described such an object. It was only much later, with the work of such people as Oppenheimer, Volkoff, and Snyder in the 1930's, that people thought seriously about the possibility that such objects might actually exist in the Universe. (Yes, this is the same Oppenheimer who ran the Manhattan Project.) These researchers showed that when a sufficiently massive star runs out of fuel, it is unable to support itself against its own gravitational pull, and it should collapse into a black hole. In general relativity, gravity is a manifestation of the curvature of spacetime. Massive objects distort space and time, so that the usual rules of geometry don't apply anymore. Near a black hole, this distortion of space is extremely severe and causes black holes to have some very strange properties. In particular, a black hole has something called an 'event horizon.' This is a spherical surface that marks the boundary of the black hole. You can pass in through the horizon, but you can't get back out. In fact, once you've crossed the horizon, you're doomed to move inexorably closer and closer to the 'singularity' at the center of the black hole. You can think of the horizon as the place where the escape velocity equals the velocity of light. Outside of the horizon, the escape velocity is less than the speed of light, so if you fire your rockets hard enough, you can give yourself enough energy to get away. But if you find yourself inside the horizon, then no matter how powerful your rockets are, you can't escape. The horizon has some very strange geometrical properties. To an observer who is sitting still somewhere far away from the black hole, the horizon seems to be a nice, static, unmoving spherical surface. But once you get close to the horizon, you realize that it has a very large velocity. In fact, it is moving outward at the speed of light! That explains why it is easy to cross the horizon in the inward direction, but impossible to get back out. Since the horizon is moving out at the speed of light, in order to escape back across it, you would have to travel faster than light. You can't go faster than light, and so you can't escape from the black hole. (If all of this sounds very strange, don't worry. It is strange. The horizon is in a certain sense sitting still, but in another sense it is flying out at the speed of light. It's a bit like Alice in "Through the Looking-Glass": she has to run as fast as she can just to stay in one place.) Once you're inside of the horizon, spacetime is distorted so much that the coordinates describing radial distance and time switch roles. That is, "r", the coordinate that describes how far away you are from the center, is a timelike coordinate, and "t" is a spacelike one. One consequence of this is that you can't stop yourself from moving to smaller and smaller values of r, just as under ordinary circumstances you can't avoid moving towards the future (that is, towards larger and larger values of t). Eventually, you're bound to hit the singularity at r = 0. You might try to avoid it by firing your rockets, but it's futile: no matter which direction you run, you can't avoid your future. Trying to avoid the center of a black hole once you've crossed the horizon is just like trying to avoid next Thursday. Incidentally, the name 'black hole' was invented by John Archibald Wheeler, and seems to have stuck because it was much catchier than previous names. Before Wheeler came along, these objects were often referred to as 'frozen stars.' The Earth is in no range of a black hole. The closest active black hole to the Milky Way Galaxy is located in the galaxy Centaurus (32 billion light years away). Therefore we have nothing to worry about relating to being sucked into the never-ending spiral of a black hole. The sun won’t become a black hole for another 4 billion years (if it does) because as you know, for a star to become a black hole it has to collapse and it has to have a solar mass of over 8. This picture shows how a black hole functions and its gravitational pull. The center of the black hole (or horizon) is the main part of black holes gravity. When a black hole forms the horizon attracts remaining gas around it and forming a spiral. The photon sphere is the far reach of gravitational pull.
Neutron Stars-Neutron Stars are the end point of a massive star's life. When a really massive star runs out of nuclear fuel in its core the core begins to collapse under gravity. When the core collapses the entire star collapses. The surface of the star falls down unti l it hits the now incredibly dense core. It then bounces off the core and blows apart in a supernova. All that remains is the collapsed core, a Neutron Star or sometimes a Black Ho le, if the star was really massive.
A typical neutron star is the size of a small city, only 10 Kilometers in diameter but it may have the mass of as many as three suns. It is quite dense. One spoonful of neutron star material on Earth would weigh as much as all the cars on Earth put togeth er.
Some neutron stars spin very rapidly and have very strong magnetic fields. If the magnetic poles are not lined up with the star's rotation axis then the magnetic field spins around very fast. Charged particles can get caught up in the magnetic fields and beem away radiation like a lighthouse lamp. This type of neutron star is called a pulsar. Pulsars are detected by their rapidly repeating radio signals beemed at Earth from those charged particles trapped in the magnetic field.
|
