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To cite the German newpaper article Astronomen beobachten erwachendes Schwarzes Loch:

Das Materie-Monster sitzt den Angaben zufolge im Herzen der 42 Millionen Lichtjahre entfernten Polarring-Galaxie NGC 660, deren Aktivität innerhalb weniger Monate Hunderte Male zugenommen hatte.

Erst wenn die Massemonster große Mengen Materie verschlucken, werden sie aktiv. Bei diesem Prozess wird so viel Energie frei, dass die Materie hell aufleuchtet, bevor sie im Schwarzen Loch verschwindet und ein Teil von ihr in Form von Jets weit ins Weltall hinaus geschleudert wird.

This translates roughly to:

According to the data the matter-monster is in the middle of the 42 million light years far away polar ring galaxy NGC 660, whose activity has increased a lot in only a few months.

Only when these Matter-monsters swallow big amounts of matter, they become active. This process releases so much energy, that it brightly enlightens the matter, before it disappears inside the black hole. A part of the matter is flung out in the universe in the form of jets.

My physics teacher told me once, that a black hole is just a very small-sized and heavy object which has so much gravity that nothing at all, not even light can't escape of its gravity. This explanation is also supported by this SE.astronomy - If nothing travels at the speed of light, except light, how can a black hole also pull light into itself? question.

  • If a "normal" (not supermassive) black hole can already prevent light to escape, how can matter which is pulled into the black hole can produce energy/light which can't escape the gravity of the black hole?

  • How can a supermassive black hole be able to pull matter, but not the light photons of the energy?

  • Additionally: Why is part of the matter which is pulled into the black hole flung (i.e. accelerated) into the universe? I understand why this matter is maybe divided - the acceleration increases as far as i know quadratic, i.e. the differences in terms of the actual acceleration, in dependence of the location may be so huge that the matter can't be held together. But i don't understand why a part of the matter is accelerated in the exact opposite direction, as a force bigger as the gravity of the supermassive black hole would be needed. Therefore: Why is a part of the matter accelerated in the opposite direction (i.e. out of the black hole's gravity) than the other part?


Note: My physics education is rather limited. I know a bit about the Newtonian gravity and a bit about the theory of Conservation of energy. But that's all I know about physics.

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It is quite correct that a black hole has so much mass that light cannot escape from a region around the black hole. The edge of this region is called the event horizon. If you cross an event horizon you are never coming back. That applies equally to light, and matter.

Around the black hole there may be matter in orbit. Since the Black hole has such strong gravity, the speed of the orbiting matter will be very fast. In fact it will be close to the speed of light. This high speed gives it lots of energy. The matter will form a disc, called an accretion disc, around the black hole, and collisions in this disc will cause the matter to heat up, to millions of degrees. At these temperatures, the disc will glow with X-rays.

On the part of the disc closest to the black hole, matter will be falling in from the disc, but before it reaches the black hole it can get enough energy to be ejected out, at very high speed, close to the speed of light. It gets ejected at right angles to the disc, at the poles of the black hole. These are the "jets". Intense radiation is produced along these jets. Blazars are distant supermassive black holes with jets that are pointed right at us.

So the black hole itself is "black", but the matter orbiting around it may be very bright.

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    $\begingroup$ @RobJeffries The blazar/quasar issue isn't entirely wrong, but it is imprecise. Quasars and blazars are both believed to be AGN (active galactic nuclei), according to the unified model. To put it simply, a quasar is an AGN distant enough for which the rest of the galaxy to not be seen, whereas a blazar is an AGN rotated in such a way that we are looking at it "jet-on". $\endgroup$ – nataliaeire Jul 22 '16 at 20:35
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The light comes from well outside the black hole event horizon.

Matter cannot fall into a black hole without first losing most of its angular momentum (otherwise it would just continue to orbit the black hole). This is accomplished by the outward transfer of angular momentum by viscosity (and other means) in an accretion disc surrounding the black hole.

As the matter gets closer to the black hole it also loses gravitational potential energy and this goes into (i) heating the gas and (ii) radiation from the gas.

At about 3 times the Schwarzschild radius of the black hole, the matter encounters the innermost stable circular orbit, which is the closest that anything with mass can make a stable orbit around a black hole. It is usually assumed that from there the material plummets into the black hole and is "lost" from our universe - increasing the mass of the black hole.

So all the radiation comes from orbiting material that is at least 3 times the Schwarzschild radius from the black hole. There is no problem for light to "escape" from this position, although it is strongly redshifted by both gravity and the transverse relativistic doppler effect.

The issue about "jets" has been covered by another question: Why do black holes have jets and accretion disks?

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Another way to put it is to think of why planets or satellites orbiting their parent don't fall into them. In a similar fashion chunks of matter swirl around the black hole. In process due to the high energy of their inertia, they emit some energy when opposed by other particles. So they shed some mass in the form of light.

It is important that we realize that it is energy with the right momentum (both direction and speed) that prepares a particle to escape the clutches of gravity. So if a particle of light has enough energy and is headed in the right direction, it will escape from its outer orbit beyond the event horizon, usually in jets.

The light emitted from such jets is of immense energy and is usually observed in the gamma spectrum. If you are interested in how these emitted jets can be used to study the black hole or in general high energy particle physics, look up, Very High Energy Gamma Ray Astronomy. There are whole classes of objects that emit VHE gamma photons and other intriguing stuff.

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