4 Weird Facts About Black Holes?

Black Holes Are Not Black

The second law of thermodynamics describes increasing entropy, or disorder, in a system, but does it apply to black holes? Physicist Jacob Bekenstein thought so, as did Hawking, who in 1974 deduced the existence of a wind of thermal radiation emanating from black holes. It subsequently became known as Hawking radiation.

How does the Hawking radiation escape? Quantum physics describes how pairs of ’virtual particles’ can pop into existence momentarily, before merging to annihilate each other.

The Universe is filled with virtual electron-positron particles that manifest out of the raw energy of space. However, if a pair of virtual particles is born on the edge of an event horizon, one of the particles can become trapped in the event horizon whilst the other moves away from it. Unable to annihilate, the virtual particle can escape, and this is what we see as Hawking radiation.

When the amount of Hawking radiation begins to overtake the amount of mass that is being swallowed up, the black hole can evaporate.

The temperature of Hawking radiation is proportional to the surface gravity of the black hole, which means that larger black holes emit relatively little Hawking radiation and are thus cold, whereas smaller black holes are hotter and evaporate at a faster rate.

Atomic-sized black holes would be 100 billion degrees Celsius and radiate within a fraction of a second.

Can Information Survive A Black Hole?

If you are swallowed up by a black hole, will any memory of your existence be retained? For three decades, scientists thought not, despite this contravening the known laws of quantum physics that suggest information, like energy and momentum, is conserved.

If information was were destroyed, there would be no way to discern what went into the black hole, or even how the black hole was made. Whatever goes in would be wiped from existence.

Stephen Hawking was the first to raise the issue of the so-called ‘information paradox’ in 1975, when he postulated that information was lost forever inside a black hole. The Hawking radiation would thus be purely thermal energy and would not retain any information on the quantum states of particles that fell into the black hole.

While at the time many scientists agreed with Hawking, doubts gradually began to emerge and in 2004 even Hawking, somewhat inexplicably, changed his mind.

If information survives intact, where does it go when it comes into contact with the singularity? Quantum gravity promises to be the key to unlocking the secrets of the singularity, and although nobody has a working model of quantum gravity yet, physicists have been working on it.

In early 2008 a team led by Abhay Ashtekar of the Penn State Institute for Gravitation and the Cosmos, used their model of quantum gravity to suggest that at the singularity lies a realm called ‘quantum space-time’.

The analogy that Ashtekar uses is to imagine that the Universe consisted of one room, with no windows or entrances. This would be space-time. Then, by opening a hidden trapdoor in the ceiling, we find a greater expanse beyond the room that we knew nothing about, and this is what he calls quantum space-time.

What this means is that at the singularity the rules of quantum physics do not stop, and information is still preserved, hidden beyond the ‘trapdoor’ in quantum space-time. Once the black hole evaporates, the information is once again revealed to the Universe.

Black Holes Can Help Create Life

Although not weird in the sense that it requires new physics to explain it, this newly found property of black holes certainly runs counter to the image we have of black holes in our heads, which is one of destruction.

Super massive black holes have powerful winds of gas that glow from the hot accretion disc that orbit them. These hot winds are capable of blowing heavy elements such as carbon and oxygen, which are crucial to life, across the Galaxy, scattering them far and wide, seeding molecular gas clouds that give rise to the next generation of stars.

Astronomers have studied the winds in a number of galaxies, including NGC 4051. The source of this wind was identified as being 2,000 Schwarzschild radii from the central black hole in that galaxy, which is equivalent to about five times the distance of Neptune from the Sun.

The observations of NGC 4051 suggest that between two and five percent of the material in the accretion disc is blown back out into the galaxy.

Infrared observations of the black holes inside distant quasars by the spectrograph instrument onboard the Spitzer Space Telescope have found ‘dust’ in the black hole’s winds, including molecules of glass, sand, even marble, rubies and sapphires!

Black Holes Might Not Exist

We’ve saved the weirdest fact for last. When describing relativity, Albert Einstein developed the idea of frames of reference.

For example, the clock onboard a spaceship will tick slower than a clock onboard a spaceship that is stationary (relative to the first craft). Thus there are two frames of reference, one onboard the moving spaceship and the other on the stationary craft. The effect of time being seen to slow down is known as time dilation and is a heavily publicised consequence of relativity.

The warping of space-time near a black hole can also cause time dilation, but in this scenario it is taken to its absolute extreme.

While an observer onboard a spacecraft falling into a black hole may see themselves fall over the event horizon, to an outside observer the spacecraft will take an infinite amount of time to cross the event horizon. In fact, an outside observer would have to wait an eternity to see the event horizon even form.

That’s not the weirdest thing. The mass of a black hole is finite, meaning that eventually it will evaporate away via Hawking radiation in a finite time.

To an outside observer, a black hole could vanish before it has even been seen to form? In that case, could it be said that the black hole ever existed in the first place?

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