- 4246 - MILKY WAY GALAXY - new discoveries? The supermassive black hole at the heart of our galaxy isn't just spinning, it's doing so at almost maximum speed, dragging anything near it along for the ride.\
----------- 4246 - MILKY WAY GALAXY - new discoveries?
- Physicists calculated the rotational speed
of the Milky Way's supermassive black hole, called Sagittarius A* (Sgr A*), by
using NASA's Chandra X-ray Observatory to view the X-rays and radio waves
emanating from outflows of material.
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- The spin speed of a black hole is defined as
"a" and given a value from 0 to 1, with 1 being the maximum
rotational speed to a particular black hole, which is a significant fraction of
the speed of light. The rotational
speed of Sgr A* is between 0.84 and 0.96.
This is close to the top limit defined by a black hole's width.
-
- Discovering that Sgr A* is rotating at its
maximum speed has far-reaching implications for our understanding of black hole
formation. A black hole's spin is
different from those of other cosmic objects. Whereas planets, stars and
asteroids are solid bodies with physical surfaces, black holes are actually
regions of space-time bounded by an outer nonphysical surface called the “event
horizon”, beyond which no light can escape.
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- While the rotation of a planet or star is
governed by the distribution of its mass, the rotation of a black hole is
described by its angular momentum. Due
to the extreme gravitational forces near a black hole, the rotation causes
spacetime to become highly curved and twisted, forming what is known as the
“ergosphere”. This effect is unique to black holes and does not occur with
solid bodies like planets or stars.
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- That means that when they spin, black holes
literally twist up the very fabric of space-time and drag anything within the
ergosphere along. This phenomenon,
called "frame dragging" or the "Lensing-Thirring effect,"
means that to understand the way space
around a black hole behaves, researchers need to know its spin. This frame
dragging also gives rise to weird visual effects around black holes.
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- As light travels close to a rotating black
hole, the rotation of spacetime causes the light's path to be curved or
twisted. This results in a phenomenon
called “gravitational lensing”, where the light's trajectory is bent due to the
gravitational influence of the rotating black hole.
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- The frame-dragging effect can lead to the
formation of light rings and even the creation of the black hole's shadow. These
are manifestations of the gravitational influence of black holes on light. The
theoretical top speed of a black hole is determined by how it feeds on matter
and thus how it grows.
-
- As matter falls into a black hole, it
increases the black hole's spin, but there's a limit to how much angular
momentum it can possess. Another factor
is the mass of the black hole. More massive black holes have a higher
gravitational pull, making it more challenging to increase their spin. Additionally, the interaction between the
black hole and its surroundings, such as accretion disks, can transfer angular
momentum and affect the black hole's spin.
-
- This could explain why Sgr A*, with its
mass equivalent to around 4.5 million suns, has a spin speed between 0.84 and
0.96 but the rapidly feeding supermassive black hole at the heart of galaxy M87
is spinning at between 0.89 and 0.91, despite having the mass of 6.5 billion
suns.
-
- The latest image from the James Webb Space
Telescope shows a portion of the dense center of our galaxy in unprecedented
detail, including never-before-seen features astronomers have yet to explain.
The star-forming region, Sagittarius C (Sgr C), is about 300 light-years from
the Milky Way's central supermassive black hole, Sagittarius A*.
-
- There's never been any infrared data on this
region with the level of resolution and sensitivity we get with Webb, so we are
seeing lots of features here for the first time. Webb reveals an incredible
amount of detail, allowing us to study star formation in this sort of
environment in a way that wasn't possible previously.
-
- The cloud the protostars at the center of
our galaxy are emerging from so dense a region that the light from stars behind
it cannot reach Webb, making it appear less crowded when it is one of the most
densely packed areas of the image.
-
- Webb's NIRCam (Near-Infrared Camera)
instrument captured large-scale emission from ionized hydrogen surrounding the
lower side of the dark cloud, shown cyan-colored in the image. This is the
result of energetic photons being emitted by young massive stars, but the vast
extent of the region shown by Webb is something of a surprise that bears
further investigation.
-
- The galactic center is a crowded,
tumultuous place. There are turbulent, magnetized gas clouds that are forming
stars, which then impact the surrounding gas with their outflowing winds, jets,
and radiation.
-
- Around 25,000 light-years from Earth, the
galactic center is close enough to study individual stars with the Webb
telescope, allowing astronomers to gather unprecedented information on how
stars form and how this process may depend on the cosmic environment,
especially compared to other regions of the galaxy. Are more massive stars
formed in the center of the Milky Way, as opposed to the edges of its spiral
arms?
-
- Massive stars are factories that produce
heavy elements in their nuclear cores, so understanding them better is like
learning the origin story of much of the universe. The Milky Way's Black Hole is spinning as
fast as it can.
-
- Pick any object in the Universe, and it is
probably spinning. Asteroids tumble end over end, planets and moons rotate on
their axes, and even black holes spin. And for everything that spins, there is
a maximum rate at which it can rotate. The black hole in our galaxy is spinning
at nearly that maximum rate.
-
- For objects such as the Earth, the maximum
rate of rotation is defined by its surface gravity. The weight we feel while
standing on the Earth isn’t just due to the gravitational pull of the Earth.
Gravity pulls us toward the center of our world, but the Earth’s rotation also
tends to fling us outward away from the Earth.
-
- This “centrifugal” force is tiny, but it
does mean that your weight at the equator is just slightly less than it is at
the north or south pole. With our
24-hour day, the weight difference between the equator and pole is just 0.3%.
But Saturn’s 10-hour day means that the difference is 19%.
-
- So much centrifugal force that that Saturn
bows outward a bit at its equator. Now imagine a planet spinning so fast that
the difference was 100%. At that point, the gravitational pull of the planet
and its centrifugal force at the equator would cancel out. If the world were to
spin any faster. it would fly apart. It would likely fly apart at an even
slower spin rate, but this is clearly the maximum rate of rotation.
-
- For black holes, things are a bit different.
Black holes aren’t objects with a physical surface. They aren’t made of
material that could fly apart. But they still have a maximum rate of rotation.
Black holes are defined by their tremendous gravity, which distorts space and
time around them. The event horizon of the black hole marks the point of no
return for nearby objects, but it isn’t a physical surface.
-
- The rotation of a black hole also isn’t
defined by the spin of physical mass, but rather by the twisting of spacetime
around the black hole. When objects such as the Earth spin, they twist space
around themselves very slightly. It’s an effect known as frame dragging.
-
- The spin of a black hole is defined by this
frame-dragging effect. Black holes spin without the physical rotation of
matter, just a twisted spacetime structure. This means there is an upper limit
to this spin due to the inherent properties of space and time.
-
- In Einstein’s equations of general
relativity, the spin of a black hole is measured by a quantity known as “a”,
where a has to be between zero and one. If a black hole has no spin, then a =
0, and if it is at its maximal rotation, then a = 1.
-
- This brings us to a new study on the
rotation of the supermassive black hole in our galaxy. The team looked at radio
and X-ray observations of the black hole to estimate its spin. Due to the
frame-dragging of spacetime near the black hole, the spectra of light from
material near it is distorted. By observing the intensity of light at various
wavelengths, the team was able to estimate the amount of spin.
-
- What they found was that the a value for our
black hole is between 0.84 and 0.96, which means it’s rotating incredibly fast.
At the upper range of the estimated rotation, it would be rotating at nearly
the maximal rate. This is even higher than the spin parameter of the black hole
in M87, where a is estimated to be between 0.89 and 0.91.
-
- A galactic archaeology project has revealed
the Milky Way’s neighboring galaxy, Andromeda, has looked at the chemical
compositions of stars in Andromeda, which is the closest large galaxy to our
own. The goal was to reconstruct its past.
-
- After examining the abundance of elements
in Andromeda and considering the fact this galaxy possesses both planetary
nebulas , gas and dust blown away from dying low-mass stars and red giant
stars, the researchers concluded that it
experienced dramatic and forceful formation.
-
- The creation of the Andromeda galaxy was
more turbulent than the origins of the Milky Way. The astronomers theorize that
Andromeda initially experienced a burst of intense star formation that created
the galaxy's foundation, with a secondary period of star birth happening
between 2 billion and 4.5 billion years ago.
-
- Although in many ways Andromeda is similar
to our own Milky Way , it's a similarly-sized, spiral disc galaxy, new
research confirms that its history is far more intense and dramatic, with
bursts of activity forming stars in abundance, and two distinct eras of star
formation.
-
- The idea is the second starburst period was
triggered when the gas-rich Andromeda collided and merged with another galaxy,
also replete with gas, in an event that astronomers call a "wet
merger." The influx of gas in such a merger acts as the fuel to kick-start
yet more bouts of star formation.
-
- Andromeda isn’t finished clashing with
other galaxies Scientists have long
thought that Andromeda experienced collisions and mergers with other galaxies
in its past, thanks to the positions and motions of its individual stars, the stars started out in another galaxy.
-
- By looking at the chemical compositions of
these stars, the team found two distinct signatures in the disc components of
Andromeda. One family of stars appeared to have ten times more oxygen than
iron, while the other group appeared to have similar amounts of both elements.
This adds a new dimension to the understanding of this galaxy’s past, revealing
more about the nature of the suggested collision and its effect on Andromeda’s
stellar population.
-
- By analyzing the chemical abundance in
different ages of stars in Andromeda, we can bring to life its history and
better understand its origins.
Andromeda likely has a history of violence and
its future looks to be equally turbulent, with our own galaxy set to
become part of its neighbor’s chaotic existence.
-
- This is because the Milky Way and Andromeda
are currently on a collision course, set to slam into each other in around 4.5
billion years. This titanic collision will give both galaxies a severe
makeover, wiping out the distinctive arms of both spiral galaxies.
-
- The stellar population of the Milky Way and
Andromeda, which is currently about 2.5 billion light years away from us, will
not slam into each other but will survive to be thrown into new orbits around a
new galactic center. Our own star, the sun, and the entire solar system are
likely to be pushed away from the new galactic core, moving toward the
outskirts of the resultant new galaxy.
-
- Oxygen is one of the so-called
alpha-elements produced by massive stars. The others are neon, magnesium,
silicon, sulfur, argon, and calcium.
Oxygen and argon have been measured with planetary nebulae, but
Andromeda is so far away that the James Webb Space Telescope (JWST) is required
to measure other elements, including iron.
-
-
November 29, 2023 MILKY WAY GALAXY
- new discoveries? 4246
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------ “Jim Detrick” -----------
--------------------- --- Wednesday, November 29,
2023
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