APOD: The Cloudy Cores of Active Galaxies (2014 Feb 24)

[APOD Robot]

The Cloudy Cores of Active Galaxies

Explanation: What would it look like to travel to the center of an active galaxy? Most galactic centers are thought to house black holes millions of times more massive than our Sun. The spaces surrounding these supermassive black holes may be far from dormant, however, flickering in many colors and earning the entire object class the title of Active Galactic Nuclei (AGN). Pictured above is a video illustrating how an active galactic nucleus may appear up close. AGN typically sport massive accretion disks feeding the central black hole, as well as powerful jets shooting electrically charged matter far into the surrounding universe. Clouds of gas and dust seen orbiting the central black holes have recently been found to be so dense that they intermittently eclipse even penetrating x-rays from reaching us. These X-ray dimming events, as short as hours but as long as years, were detected in an analysis encompassing over a decade of data taken by the NASA's orbiting Rossi X-ray Timing Explorer (RXTE).

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[Beyond]

What would it look like to travel to the center of an active galaxy? I should think that you would see yourself being radiated to a crisp!

[geckzilla]

Only if you got too close. Just bring the ship nearby and then remember the instructions about not looking directly at the sun or nucleus of an accretion disk through your telescope.

[Ann]

I think it might be dangerous to look down the jet of an active galaxy.

Ann

[Sinan İpek]

I think you should have two Hubble telescopes instead of eye balls in order to see it like in this movie! With your humlble, god's gift eyes, you see only black space and stars!

[BDanielMayfield]

I think it might be dangerous to look down the jet of an active galaxy.

Ann

For sure, and not just looking down the jet. It wouldn't be wise to fly across it ether!

Bruce

[Beyond]

I think it might be dangerous to look down the jet of an active galaxy.

Ann

"Assault by a black hole." Sounds more like a science fiction movie than a NASA discovery.

[orin stepanek]

Aw; you'd die of old age before you got close enough to look at it!

[BDanielMayfield]

Aw; you'd die of old age before you got close enough to look at it!

But aging is only a temporary problem.

Bruce

[Beyond]

Aw; you'd die of old age before you got close enough to look at it!

But aging is only a temporary problem.

Bruce

Yeah, it's like being always stuck-in-the-mud. It sucks and you can't get out of it, until...

[Spif]

I think it might be dangerous to look down the jet of an active galaxy.

Ann

For sure, and not just looking down the jet. It wouldn't be wise to fly across it ether!

I wonder what the numbers are like... energy flux and particle flux?

I recall vaguely from my high energy astro class (a couple decades ago) that there is supposed to be a stream of electrons that are highly relativistic. Presumably there are protons too? EM Radiation?

Protons and gamma rays can be penetrating but I think electrons would at most produce a heating effect on a spacecraft?

-s

[neufer]

Protons and gamma rays can be penetrating but I think electrons would at most produce a heating effect on a spacecraft?

The proton flux has to match the electron flux to keep electrical neutrality.

A proton moving at the same velocity as an electron packs a lot more energy.

[Beyond]

Protons and gamma rays can be penetrating but I think electrons would at most produce a heating effect on a spacecraft?

The proton flux has to match the electron flux to keep electrical neutrality.

A proton moving at the same velocity as an electron packs a lot more energy.

Because it's a lot bigger?, diminutively speaking.

[Boomer12k]

Don't forget the SPF 1,000,000,000,000....

:---[===] *

[Chris Peterson]

The proton flux has to match the electron flux to keep electrical neutrality.

A proton moving at the same velocity as an electron packs a lot more energy.

Because it's a lot bigger?, diminutively speaking.

Not bigger, but more massive. About 1800 times more massive, which means 1800 times more kinetic energy for a given velocity.

[Beyond]

Heh, i almost said massive, but for us non-scientific folks, it's included in 'bigger'.
So a proton and electron are physically the same size?

[neufer]

So a proton and electron are physically the same size?

The electron is generally considered to be a fundamental point particle and hence has no size.

The proton is considered to be a composite of 3 fundamental point particles (i.e., quarks)
which orbit about each other giving the proton a size of about 10^-13 cm.

[Chris Peterson]

Heh, i almost said massive, but for us non-scientific folks, it's included in 'bigger'.
So a proton and electron are physically the same size?

Subatomic particles don't really have sizes in the classical sense. An electron is believed to have no internal structure, so it is considered to have no size- a volumeless point. A proton is made up of quarks, and has a sort of size, called a charge radius. Really, though, at the quantum scale "size" is usually not very meaningful. The properties that define behavior are different- charge, rest mass, angular momentum, and others.

[Spif]

Heh, i almost said massive, but for us non-scientific folks, it's included in 'bigger'.
So a proton and electron are physically the same size?

Subatomic particles don't really have sizes in the classical sense. An electron is believed to have no internal structure, so it is considered to have no size- a volumeless point. A proton is made up of quarks, and has a sort of size, called a charge radius. Really, though, at the quantum scale "size" is usually not very meaningful. The properties that define behavior are different- charge, rest mass, angular momentum, and others.

My understanding is that particles do have "cross sections" ... which is a statistically typical interaction radius that reflects the likelihood of the particle reacting with something when it comes close. I believe collision cross sections can vary depending on the particular force involved in the interaction and with the properties of the particles involved. Cross section can be thought of as an effective size.

As I recall then, in regard to cross section, electrons are considered to be quite large and puffy because they are light and yet they are very likely to interact with other charged particles and thereby suffer a "collision".

But I never took a particle physics or a QCD class... Maybe someone can fill in more in that regard.

In my limited understanding of quantum mechanics, string theories notwithstanding, fundamental particles aren't really physical balls of stuff with a physical radius. Rather, they are more like roving probability waves. When the probability wave of one particle overlaps with the probability wave from another particle, there is a chance that the two will interact dramatically (ie: collision). The chance of an interaction increases with the amplitude of each probability wave in the areas where the waves overlap significantly.

(Technically, all particles have wave functions that extend to infinity (as big as the universe), but at some point their wave function amplitude becomes so infinitesimally small that an interaction is unlikely to occur even once in a period of time equal to the age of the universe, effectively "never".)

-s

[Anthony Barreiro]

...
In my limited understanding of quantum mechanics, string theories notwithstanding, fundamental particles aren't really physical balls of stuff with a physical radius. Rather, they are more like roving probability waves. When the probability wave of one particle overlaps with the probability wave from another particle, there is a chance that the two will interact dramatically (ie: collision). The chance of an interaction increases with the amplitude of each probability wave in the areas where the waves overlap significantly.

(Technically, all particles have wave functions that extend to infinity (as big as the universe), but at some point their wave function amplitude becomes so infinitesimally small that an interaction is unlikely to occur even once in a period of time equal to the age of the universe, effectively "never".)

-s

That's a lovely description. I probably learned more from your educated layperson's explanation than I would learn from experts whose knowledge is so complex that they can't put it into simple terms. Plus, they would be arguing with one another about subtleties that are totally beyond my simple understanding.

I love that quantum mechanics is probablistic rather than deterministic. Anything can happen, although some things are more likely than others, and at either extreme there are the practical limits of "virtually certain" and "virtually impossible."

[Chris Peterson]

I love that quantum mechanics is probablistic rather than deterministic. Anything can happen, although some things are more likely than others, and at either extreme there are the practical limits of "virtually certain" and "virtually impossible."

Indeed. Your wavefunction extends very far (but probably not infinitely far). At any moment, you could find yourself unexpectedly on the Moon, without having to pass through the intervening space. How convenient. Briefly. Of course, statistically, only part of you would end up there. Quantum travel can get messy.

[Beyond]

I love that quantum mechanics is probablistic rather than deterministic. Anything can happen, although some things are more likely than others, and at either extreme there are the practical limits of "virtually certain" and "virtually impossible."

Indeed. Your wavefunction extends very far (but probably not infinitely far). At any moment, you could find yourself unexpectedly on the Moon, without having to pass through the intervening space. How convenient. Briefly. Of course, statistically, only part of you would end up there. Quantum travel can get messy.

"Messy", a neat and tidy word for it.

[Anthony Barreiro]

I love that quantum mechanics is probablistic rather than deterministic. Anything can happen, although some things are more likely than others, and at either extreme there are the practical limits of "virtually certain" and "virtually impossible."

Indeed. Your wavefunction extends very far (but probably not infinitely far). At any moment, you could find yourself unexpectedly on the Moon, without having to pass through the intervening space. How convenient. Briefly. Of course, statistically, only part of you would end up there. Quantum travel can get messy.

Oh, but we're so much bigger and more complicated than a photon or electron. Who knows where they're popping in and out of reality, like tiny Dr. Who's?

[Chris Peterson]

Oh, but we're so much bigger and more complicated than a photon or electron. Who knows where they're popping in and out of reality, like tiny Dr. Who's?

Just means you have to wait longer.

I should point out that this very communication is dependent upon the ability of electrons to disappear and reappear at a quantum level (many of the devices in your computer depend on quantum tunneling, as do many imaging devices).

[BDanielMayfield]

Warning to Starship Crew: When contemplating piloting our ship or a shuttle craft into the jet of an active galactic nuclei, pilots must consider cosmic rays.

Cosmic rays are very high-energy particles, mainly originating outside the Solar System. They may produce showers of secondary particles that penetrate and impact the Earth's atmosphere and sometimes even reach the surface. Composed primarily of high-energy protons and atomic nuclei, they are of mysterious origin. Data from the Fermi space telescope (2013) have been interpreted as evidence that a significant fraction of primary cosmic rays originate from the supernovae of massive stars. However, this is not thought to be their only source. Active galactic nuclei probably also produce cosmic rays...

Cosmic rays attract great interest practically, due to the damage they inflict on microelectronics and life outside the protection of an atmosphere and magnetic field, and scientifically, because the energies of the most energetic ultra-high-energy cosmic rays (UHECRs) have been observed to approach 3 × 1020 eV, about 40 million times the energy of particles accelerated by the Large Hadron Collider...

Of primary cosmic rays, which originate outside of Earth's atmosphere, about 99% are the nuclei (stripped of their electron shells) of well-known atoms, and about 1% are solitary electrons (similar to beta particles). Of the nuclei, about 90% are simple protons, i. e. hydrogen nuclei; 9% are alpha particles, and 1% are the nuclei of heavier elements.

And by all means, make sure shields are at full power.