- 4398 - BLACKHOLES - why they do exist? Blackholes in space are where gravity has gotten so strong it collapses the atoms of all matter. Here are the ways that black holes really do exist There is significant evidence to prove they are real.
------------------------- 4398 -
BLACKHOLES - why they do exist?
-
- Of all the far-out concepts in astronomy,
black holes may be the weirdest. A region of space where matter is so tightly
packed that nothing, not even light itself, can escape. With all the normal rules of physics breaking
down inside them, it's tempting to dismiss black holes as the stuff of science
fiction. Yet there's plenty of evidence that they really do exist in the
universe.
-
- Black holes were found to be an inevitable
consequence of Albert Einstein's theory of general relativity. As a theoretical
possibility, black holes were predicted in 1916 by Karl Schwarzschild, who
found them to be an inevitable consequence of Einstein's theory of general
relativity. If Einstein's theory is correct, and all the evidence suggests it
is, then black holes must exist.
-
- Blackholes were put on even firmer ground
by Roger Penrose and Stephen Hawking, who showed that any object collapsing
down to a black hole will form a “singularity” where the traditional laws of
physics break down. This has become so widely accepted that Penrose was awarded
a share in the 2020 Nobel prize in physics "for the discovery that black
hole formation is a robust prediction of the general theory of
relativity."
-
- In the 1930s, Indian astrophysicist
Subramanian Chandrasekhar looked at what happens to a star when it has used up
all its nuclear fuel. The end result, he found, depends on the star's mass. If
that star is really big, say 20 solar masses, then its dense core, which may
itself be three or more times the mass of the sun, collapses all the way down
to a black hole.
-
- The final core collapse happens incredibly
quickly, in a matter of seconds, and it releases a tremendous amount of energy
in the form of a gamma-ray burst. This burst can radiate as much energy into
space as an ordinary star emits in its entire lifetime. And telescopes on Earth
have detected many of these bursts, some of which come from galaxies billions
of light-years away; so we can actually see black holes being born.
-
- Black holes don't always exist in
isolation. Sometimes they occur in
pairs, orbiting around each other. When they do, the gravitational interaction
between them creates ripples in space-time, which propagate outward as
gravitational waves, another prediction of Einstein's theory of relativity.
-
- With observatories like the “Laser
Interferometer Gravitational-Wave Observatory and Virgo”, we now have the
ability to detect these waves. The
first discovery, involving the merger of two black holes, was announced in
2016, and many more have been made since then. -
- As detector sensitivity improves, other
wave-generating events besides black hole mergers are being discovered, such as
a crash between a black hole and a neutron star, which took place way beyond
our own galaxy at a distance of 650 million to 1.5 billion light-years from
Earth.
-
- The short-lived, high-energy events that
produce gamma-ray bursts and gravitational waves may be visible halfway across
the observable universe, but for most of their lives black holes, by their very
nature, will be almost undetectable. The fact that they don't emit any light or
other radiation means they could be lurking in our cosmic neighborhood without
astronomers being aware of it.
-
- There's one sure-fire way to detect the
dark beasts and that's through their gravitational effects on other stars. When
observing the ordinary-looking binary system, or pair of orbiting stars, known
as “HR 6819” in 2020, astronomers noticed oddities in the motion of the two
visible stars that could be explained only if there was a third, totally
invisible, object there.
-
- When they worked out its mass, at least
four times that of the sun, the researchers knew there was only one possibility
left. It had to be a black hole. It is
the closest yet discovered to Earth, a mere thousand light-years away inside
our own galaxy.
-
- The first observational evidence for a
black hole emerged in 1971, and this too came from a binary star system within
our own galaxy. “Cygnus X-1”, the
system produces some of the universe's brightest X-rays. These don't emanate
from the black hole itself, or from its visible companion star, which is
enormous, at 33 times the mass of our own sun.
Rather, matter is constantly being stripped from the giant star and
dragged into an accretion disk around the black hole, and it's from this
accretion disk that the X-rays are emitted.
-
- As they did with “HR 6819”, astronomers can
use observed star motion to estimate the mass of the unseen object in Cygnus
X-1. The latest calculations put the dark object at 21 solar masses
concentrated into such a small space that it couldn't be anything other than a
black hole.
-
- In addition to black holes created through
stellar collapse, supermassive black holes, each millions or even billions of
solar masses, have been lurking in the centers of galaxies since early in the
history of the universe. In the case of active galaxies, the evidence for these
heavyweights is spectacular.
-
- The central black holes in these galaxies
are surrounded by accretion disks that produce intense radiation at all
wavelengths of light. We also have evidence that our own galaxy has a black
hole at its center. That's because we see the stars in that region whizzing
around so fast, up to 8% of the speed of light, that they must be orbiting
something extremely small and massive. Current estimates put the Milky Way's
central black hole somewhere around 4 million solar masses.
-
- Another piece of evidence for the existence
of black holes is … spaghettification. Spaghettification is what happens when
you fall into a black hole, and it's pretty self-explanatory. You get stretched
out into thin strands by the black hole's extreme gravitational pull. Luckily,
that's not likely to happen to you or anyone you know, but it may well be the
fate of a star that wanders too close to a supermassive black hole.
-
- In October 2020, astronomers witnessed this
shredding and saw the flash of light from a hapless star as it was ripped
apart. Fortunately, the spaghettifying didn't happen anywhere near Earth, but
instead in a galaxy 215 million light-years away.
-
- So far we've had plenty of compelling
indirect evidence for black holes: bursts of radiation or gravitational waves,
or dynamical effects on other bodies, that couldn't have been produced by any
other object known to science. But the final clincher came in April 2019, in
the form of a direct image of the supermassive black hole at the center of
active galaxy Messier 87.
-
- The Event Horizon Telescope consists of a large network of telescopes
scattered all over the world rather than a single instrument. The more telescopes that can participate,
and the more widely spaced they are, the better the final image quality. The
result clearly shows the dark shadow of the 6.5 billion-solar-mass black hole
against the orange glow of its surrounding accretion disk.
-
- Black holes not only existed at the dawn of
time, they birthed new stars and supercharged galaxy formation according to a
new analysis of James Webb Space Telescope data. These insights upend theories
of how black holes shape the cosmos, challenging classical understanding that
they formed after the first stars and galaxies emerged. Instead, black holes
might have dramatically accelerated the birth of new stars during the first 50
million years of the universe, a fleeting period within its 13.8 billion-year
history.
-
- We know these monster black holes exist at
the center of galaxies near our Milky Way, but the big surprise now is that
they were present at the beginning of the universe as well and were almost like
building blocks or seeds for early galaxies.
They boosted everything, like gigantic amplifiers of star formation,
which is a whole turnaround of what we thought possible before so much so that
this could completely shake up our understanding of how galaxies form.
-
- Distant galaxies from the very early
universe, observed through the Webb telescope, appear much brighter than
scientists predicted and reveal unusually high numbers of young stars and
supermassive black holes. Conventional
wisdom holds that black holes formed after the collapse of supermassive stars
and that galaxies formed after the first stars lit up the dark early universe.
-
- But the analysis suggests that black holes
and galaxies coexisted and influenced each other's fate during the first 100
million years. If the entire history of the universe were a 12-month calendar,
those years would be like the first days of January.
-
- Black hole outflows crushed gas clouds,
turning them into stars and greatly accelerating the rate of star
formation. Black holes are regions in
space where gravity is so strong that nothing can escape their pull, not even
light. Because of this force, they generate powerful magnetic fields that make
violent storms, ejecting turbulent plasma and ultimately acting like enormous
particle accelerators. This process is likely why Webb's detectors have spotted
more of these black holes and bright galaxies than scientists anticipated.
-
- We can't quite see these violent winds or
jets far, far away, but we know they must be present because we see many black
holes early on in the universe. These
enormous winds coming from the black holes crush nearby gas clouds and turn
them into stars. That's the missing link that explains why these first galaxies
are so much brighter than we expected.
-
- During the first phase, high-speed outflows
from black holes accelerated star formation, and then, in a second phase, the
outflows slowed down. A few hundred million years after the big bang, gas
clouds collapsed because of supermassive black hole magnetic storms, and new
stars were born at a rate far exceeding that observed billions of years later
in normal galaxies. The creation of stars slowed down because these powerful
outflows transitioned into a state of energy conservation reducing the gas available
to form stars in galaxies.
-
- We thought that in the beginning, galaxies
formed when a giant gas cloud collapsed.
The big surprise is that there was a seed in the middle of that cloud—a
big black hole—and that helped rapidly turn the inner part of that cloud into
stars at a rate much greater than we ever expected. And so the first galaxies
are incredibly bright.
-
- The James Webb Space Telescope is probing
galaxies near the dawn of time. One of these is the exceptionally luminous
galaxy “GN-z11”, which existed when the universe was just a tiny fraction of
its current age. Initially detected with the NASA/ESA Hubble Space Telescope,
it is one of the youngest and most distant galaxies ever observed, and it is
also one of the most enigmatic. Why is it so bright? Webb appears to have found
the answer.
-
- A team studying GN-z11 with Webb found the
first clear evidence that the galaxy is hosting a central, supermassive black
hole that is rapidly accreting matter. Their finding makes this the most
distant active supermassive black hole spotted to date.
-
- Using Webb, the team also found
indications of ionized chemical elements typically observed near accreting
supermassive black holes. They
discovered that the galaxy is expelling a very powerful wind. Such
high-velocity winds are typically driven by processes associated with
vigorously accreting supermassive black holes.
-
- The fact that we don't see anything else
beyond helium suggests that this clump must be fairly pristine. This is something that was expected by theory
and simulations in the vicinity of particularly massive galaxies from these
epochs that there should be pockets of pristine gas surviving in the halo, and
these may collapse and form Population III star clusters.
-
- Finding the so far unseen Population III
stars, the first generation of stars formed almost entirely from hydrogen and
helium, is one of the most important goals of modern astrophysics. These stars
are expected to be very massive, very luminous, and very hot. Their signature
would be the presence of ionized helium and the absence of chemical elements
heavier than helium.
-
- The formation of the first stars and galaxies
marks a fundamental shift in cosmic history, during which the universe evolved
from a dark and relatively simple state into the highly structured and complex
environment we see today.
-
-
March 21, 2023 BLACKHOLES - why
they do exist? 4398
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