a black hole emits no radiation. How do astronomers know they exist if they are invisible?

Answer 1

Not quite true; while the gravitational field is so immense within the event horizon of a black hole that even light cannot escape it, two different phenomena occur right at the event horizon which provide astronomers with secondary evidence of their presence. Firstly, all the matter a black hole consumes becomes accelerated by its gravitational pull. If the matter is a charged particle, acclerating it creates a changing electric and magnetic field around it, which propagates as electromagnetic radiation -- basically light. Up until the point where it crosses the event horizon, it continues to emit EM radiation which may be detectable from Earth (if enough particles are accelerated at once) Secondly, there's "Hawking radiation:" the intense curvature of space-time at the event horizon of a black hole causes virtual particles to pop into existence -- a pair, actually, one particle and it's corresponding antiparticle (being opposites, they cancel each other out energy-wise and the universe is still balanced) In the rest of the universe, when a virtual particle pair appears, the two opposite charges annihilate one another in a (tiny) flash of light, but at the event horizon, there's a good chance that one of the two gets sucked into the black hole while the other goes zinging off in the opposite direction, effectively adding to the mass of the universe. So a stream of subatomic particles can also sometimes be detected from a black hole.

Also, because black holes ARE such a big gravity well, they affect stars more distant from us than the black hole is by allowing us to see them via gravitational lensing -- the gravity is enough to bend light from stars that are beyond it enough so that we can see them, but there is a detectable distortion to the image that astronomers can use to determine where the mass causing the lensing is located, and based on what we know of the stars beyond it, can calculate its mass... and if the number they get is huge like a red giant star yet it doesn't glow, that's another good indicator of a black hole in the neighborhood.

Answer 2

Many black holes have disks of dust and debris swirling around them at high speeds, called accretion disks. When this matter gets close enough to the event horizon such that it's sucked in, this processes is so violent it often generates radiation such as x-rays and perhaps gamma rays. The x-rays have not yet crossed the point of no return and so do not actually come from what we consider within the black hole.

These disks can be very active and can often times be easily observable with the proper instruments.

Black holes do emitt a particular type of radiation called Hawking Radiation, however the radiation doesn't escape in the conventional way. It instead escapes in a quantum way called "tunneling".

Answer 3

It will affect other bodies of mass around it. Sometimes astronomers will see a star orbitting something that doesn't seem to exist. You can see a black hole if it passes through a clump of matter. It will pull atoms toward it. They will gain kinetic energy from this pull and heat up. When atoms reach really high temperatures, they emit x-rays. So anywhere in space that has a large concentration of x-rays can be suspected to have a black hole nearby. There's a supermassive black hole at the center of our galaxy.

Answer 4

scientist know that blackholes exist because...
1. when scientist flashes a beam of light to blackholes, they do not shine back since the gravity in these objects are so extreme that light cannot escape unlike objects like stars, galaxies, asteroids.
2. they affect the orbit of stars and other heavenly objects. By determining the weird wobble of the heavenly objects, scientist can calculate the exact position of blackholes even they are invincible. basic physics, vector addition.
3. blackholes are enourmus and can swallow almost anything and they can swallow stars if the stars are close enough so scientist can predict the there is blackhole if star vanishes..

Answer 5

The know they are there by how other bodies react inproximity to them. ie if a comet strays nearby they can determine that there is gravitational pull on it from a certain point, when there is nothing in the region which should be exerting this gravitational pull they may have identified a black hole.

Answer 6

You just answered your own question... beccause there is NOTHING in a black hole, they can discover it by looking at the nothingness... They know a black hole is there because there is no radiation and no light comes from it..:P

Answer 7

there are truly many procedures :- a million. often few stars revolve around a black hollow and as all of us comprehend any merchandise in area revolves in user-friendly terms around a extra vast merchandise. so scientists determine that there must be a black hollow this is making it revolve around itself 2.gravitational magnification additionally helps. in accordance to einstien's area time graph any gentle ray while passes close to a great physique a megastar or a black hollow it truly is magnified . there's a fastened shrink magnification above this is basically too intense for any wide-spread spacious merchandise . so it truly is inferred that a black hollow must be there

Answer 8

the void that is a black hole

the absence of radiation is what astronomers detect

Answer 9

because of gravity, the force of gravity inside a black hole is able to bend light passing a black hole . it is this distortion in light that enables to detect a black hole

Answer 10

You obviously have never placed a bet on the Saints....Same principal!