- 3867 - QUASARS - blackhole center of galaxies. Discovered 60 years ago quasars have a misleading name. While these objects do shine like a star from our eyes on Earth, they are the brightest objects in the universe. They’re actually the ultra-bright centers of galaxies powered by powerful supermassive black holes.
----------- 3867 - QUASARS - blackhole center of galaxies?
- A “quasar” today is an active galactic
nucleus, or a galaxy that has a nucleus with high luminosity in parts of the
electromagnetic spectrum. Supermassive black holes can be between millions to
billions of times the mass of the Sun.
One exists at the center of every large galaxy.
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- The first hints of quasars came in 1908,
when Edward Arthur Fath noticed increased luminosity in the center of what were
then considered nebulae. Vesto Slipher also examined light spectra from
different nebulae and determined that they had unusually bright emission lines.
However, they noticed that some emission lines were thick, indicating a range
of wavelengths.
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- Then in 1918, Hebert Curtis was observing
the central object in the Virgo cluster, Messier 87, which famously became home
to the image of the first black hole, and he saw a jet coming out of the center
of the object, but he had no idea what it was. It was the first observation of
an active galactic nucleus jet.
-
- Astronomers didn’t know that nebula and
galaxies were not, in fact, one and the same.
Harlow Shapley and Heber Curtis in the 1920s had this big debate about
are the spiral nebulae inside our galaxy or they whole separate island
universes, island universes?
-
- By the 1930s, we understood thanks to the
work of Edwin Hubble that a lot of these smaller nebulae were analogous to our
entire Milky Way Galaxy, and were much further away.
-
- In 1943, Carl Seyfert published a list of
galaxies with enhanced activity at their centers, bright spots and fat emission
lines. In 1944, radio astronomy was starting up, and scientists started to look
for radio signals in the sky.
-
- In the 1950s, John Bolton, Gordon Stanley, and Owen Slee
were trying to chase down these radio sources using the Parkes Radio Telescope
in Australia. They found that tiny distant galaxies were associated with some
of the brightest radio sources, which didn’t make much sense to them at the
time. These observations were
confirmed in 1962.
-
- In 1963 Martin Schmidt performed follow-up
work on the spectra of the galaxies to confirm that the bright radio sources
and galaxies were likely one and the same.
-
- Eventually, it was suggested that these
types of phenomena might be associated with supermassive black holes at the
center of a galaxy. There wasn't any
consensus. It really took six years to figure out that these, whatever the hell
these things are, they probably must involve a very dense massive object in the
center of a galaxy.
-
- We had a lot of different names for a lot
of basically similar things in different ways.
Active galactic nucleus is a good term for any of these objects that
basically are quasars with accreting material, releasing energy, releasing
energy. And the amount of the efficiency can vary the size can vary the mask or
vary, but it pretty much scales.
-
- While
small black holes and supermassive black holes share similar behaviors, they
have a different formation process.
They're the same physics because the physics of black holes is just the
theory of gravity. But, there are two
ways of squishing something that much, and one of them is killing a star and
the other is collapsing part of space-time in the early Universe.
-
- Supermassive black holes are are ultimately
thought to be essential components of a galaxy’s creation and evolution. The supermassive black hole is the nucleus
of the galaxy, surrounded by a galaxy of stars, which is then surrounded by a
halo of dark matter. Matter is attracted to the center, but often misses the
center of the black hole and instead goes into orbit around it, piling up,
lumping together, and forming an accretion disk.
-
- As the matter orbits the black hole, there
is friction within the accretion disk, which makes the matter radiate energy
and spiral slowly towards its center; the matter very gradually moving towards
the edge of the black hole.
-
- Orbital speeds increase progressively as
the matter approaches the black hole, eventually approaching the speed of
light. Once that universal speed limit is reached, though, matter is sucked
into the supermassive black hole.
-
- The process generates heat, and friction,
so the disc shines. The closer you are to the black hole, the faster you're
going, the hotter you get. What happens
in a certain set of supermassive black holes, is that the black hole is a messy
eater, some stuff goes down the black hole, but other stuff, if the disc isn't
too thick, you can actually sustain a magnetic field or kind of magnetosphere,
around the black hole.
-
- If the back of the black hole is spinning
quite fast, the rotational speed of the event horizon in some senses is
spinning near the speed of light and the magnetosphere is spinning, and it
catches light, maybe 10 percent of the material shoots it out the north and
south poles at speeds close to the speed of light.
-
- Not
only are quasars the brightest objects in the universe, but you see
relativistic phenomena associated with them. Because of that, it means they are
an extreme physics phenomena and strong gravity phenomena that involve general
relativity, and special relativity.
-
- Different terms are used to imply the
total luminosity output of an active galactic nuclei, with quasars being the
brightest and are more distant. Their
distance and age can be measured by how much their radiation is redshifted.
They are often much brighter than the rest of their host galaxy.
-
- Another type of galactic nuclei are
Seyfert galaxies, which are less luminous and tend to be closer. It is
generally thought that Seyfert galaxies are younger. They interact in a way that at a certain
point, you feed the quasar enough that it has a big radiation; stuff comes out
and a big jet comes out and blows out the gas that would make more stars, and
switches star formation off. “So,
there's a feedback mechanism.”
-
February 8, 2023 QUASARS -
blackhole center of galaxies
3867
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--- Thursday, February 9, 2023 ---------------------------
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