- 4363 - BLACKHOLE - what was the earliest found? How do you build a giant black hole in the early universe? Start with the explosions of lots of little ones. James Webb Space Telescope (JWST) has revealed ironclad evidence that the young universe was populated by incredibly massive black holes.
-------------- 4363 - BLACKHOLE - what was the earliest found?
- Although
astronomers can't see the black holes directly, they do observe quasars which
are ultrabright objects powered by supermassive black holes. When material
falls onto such a giant black hole, the material compresses and heats up,
releasing an enormous amount of energy.
Quasars stand as the most powerful engines in the entire universe,
capable of outshining thousands of galaxies at once and lasting millions of
years.
-
- Astronomers can
see these giant cosmic lighthouses from across the universe, including at the
earliest times of star and galaxy formation. The oldest known quasar existed
when our universe was only a few hundred million years old.
-
- The existence of
old quasars means that supermassive black holes also had to exist, but this
idea poses a challenge for our current understanding of galaxy growth. As far
as we know, the only way to make black holes is through the deaths of massive
stars. But these leave behind black holes with masses of only a few times that
of the sun. To make a quasar, a black hole has to be at least a few million
times the mass of the sun.
-
- But the quasars are
appearing so early in the cosmic record that there isn't enough time for the
first stars to be born and die, and then allow their remnant black holes to
merge and accumulate gas to grow to supermassive status.
-
- Rare black hole 1
billion times the mass of the sun could upend our understanding of galaxy
formation. One potential way to build
giant black holes in the early universe is to skip the whole star-formation bit
and just allow huge clouds of hydrogen gas to collapse on their own directly
into a black hole.
-
- To make a giant
cloud of hydrogen collapse, you have to get rid of its heat. But cool hydrogen
has an annoying habit of turning from free hydrogen atoms into diatomic
hydrogen molecules. Hydrogen molecules
are really good at cooling themselves off by emitting radiation.
-
- In the traditional
scenario, before the atomic hydrogen gas cloud has a chance to collapse into a
singular black hole, it fragments into many smaller pockets of molecular
hydrogen, each of which collapses, forming a bunch of stars instead.
-
- The trick is to
get the giant cloud of hydrogen to cool off,
but not so quickly that the whole thing becomes a single supermassive
black hole. That's where tiny black holes come to the rescue.
-
- The physics of the
early universe within the first few seconds of the Big Bang are so intense that
the cosmos may have directly produced innumerable small black holes that formed
through the frothing and seething foam that was space-time itself. These small
black holes don't live forever, though; they evaporate through the emission of
Hawking radiation, and likely only a small fraction of them have survived to
the present day.
-
- But in that early
epoch of the universe, the first stars, galaxies and black holes may have been
much more abundant. As they evaporated, they emitted radiation, and the
researchers discovered that these small black holes could release just the
right amount of heat to keep a giant gas cloud from fragmenting into molecular
hydrogen clumps, thus allowing the cloud to slowly and steadily collapse into a
single giant black hole.
-
- This result is
interesting because it does not invoke even more exotic forms of energy release
or the addition of new forces of nature. It also shows how even relatively
straightforward physics can interact in strange and unfamiliar ways in the
early universe.
-
- A newly discovered
mystery object could be the heaviest neutron star ever seen, the smallest black
hole, or something completely new to science.
Astronomers have spotted this mysterious cosmic object that could be the
lightest black hole or the heaviest neutron star ever discovered.
-
- The unknown
object, discovered 40,000 light-years away inside a dense globule of stars
named “NGC 1851”, was detected through the rapid flashes of its orbiting
companion, a rotating neutron star known as a pulsar that sweeps out a beam of
light once every 6 milliseconds.
-
- This new entity
falls within the historical "mass gap" between black holes and
neutron stars, meaning it could be either one.
This pulsar-black hole system will be an important target for testing
theories of gravity and a heavy neutron star will provide new insights in
nuclear physics at very high densities.
-
- Both black holes
and neutron stars are stellar corpses, left behind after massive stars end
their lives in violent explosions called supernovas. Despite being born the
same way the two types of objects can have vastly different masses. Supermassive black holes can weigh as much
as billions of suns, while neutron stars rarely get heavier than about three
solar masses. But the lightest black holes and the heaviest neutron stars can
look very similar.
-
- For most of
astronomy's history, scientists could only spot neutron stars as heavy as twice
the mass of the sun and black holes as light as five solar masses, leaving
everything in between a mystery. The gap between the two, known as the “mass
gap”, was finally crossed in 2019, when the Laser Interferometer
Gravitational-Wave Observatory (LIGO) detected space-time ripples indicative of
a light black hole or heavy neutron star falling somewhere between the two. Detections of mass-gap-filling objects through
conventional light-based telescopes have remained elusive.
-
- To spot the new
object, astronomers used the “MeerKAT radio telescope” in South Africa to scan
the “NGC 1851” globular cluster. This is
a crowded blob of stars so tightly packed that the cosmic furnaces may
sometimes knock one another from their orbits and even collide.
-
- Faint radio pulses
repeating 170 times a second drew the astronomers' attention to a pulsar, and
by observing the subtle changes to its highly regular "ticks," the
scientists mapped out its orbital motion. This revealed that the pulsar was in
a binary system, orbiting an object of roughly 3.9 solar masses in the middle
of the mass gap.
-
- What the object
could be? The most massive neutron star
known, the lightest black hole, or some yet-to-be-characterized exotic star
husk is unclear. Uncovering the true
nature of the companion will be a turning point in our understanding of neutron
stars, black holes, and whatever else might be lurking in the black hole mass
gap.
-
- What's the biggest
black hole in the universe. On the other
extreme is there a limit to how big black holes can get? Black holes are some of the most massive
single objects in space, but what's the biggest one in existence, and how big
can they get?
-
- This monster, “TON
618”, weighs roughly 40 billion solar masses. TON 618 has a radius of over
1,000 astronomical units (AU), which means that if the black hole was placed in
the center of the solar system, by the time you reached Pluto, you would be
less than 5% of the way from the center of the black hole to its edge.
-
- TON 618 sits about
18.2 billion light-years away from Earth. In the night sky, it sits on the border between the constellations
Canes Venatici and Coma Berenices. Astronomers first spotted it in a 1957
survey but didn’t realize what it was. They first thought it was a faint blue
star, but observations a decade later revealed that the astronomers had
glimpsed intense radiation from the material falling into the giant black hole.
-
- TON 618 powers a
quasar, one of the brightest objects in the entire universe with the
illuminating power of 140 trillion suns. Quasars draw light from the
gravitational energy of the central black hole. Material around the black hole
falls in, and as it does so it compresses and heats up, releasing enormous
amounts of radiation.
-
- While individual
events like the most powerful supernovas can briefly outshine quasars, they
only last a few weeks. In contrast, quasars can shine for millions of
years. However, quasars are so far away
that they only appear as faint spots of visible light in even the most powerful
telescopes, and astronomers first detected them by their powerful radio
emissions.
-
- Quasars are
supermassive black holes that are feeding. Supermassive black holes become
enormous through a combination of merging with other black holes and by
constantly feeding on surrounding material.
This feeding rate is what sets the limit on the size of a black hole.
-
- These cosmic
vacuum cleaners can only consume so much material in a given amount of time. As
material falls in, it heats up and releases radiation (creating a quasar), but
that radiation heats the material itself, preventing it from quickly falling
into the black hole. This self-regulation prevents black holes from growing too
quickly. -
- Astronomers can
estimate a maximum mass for a black hole by taking that feeding rate and
multiplying it by the known age of the universe, giving an estimated maximum
mass of around 50 billion solar masses.
However, that is only an estimate. There may be other, more exotic, ways
to create large black holes, such as from the direct collapse of large clumps
of dark matter in the early universe.
-
-
February 22, 2024
4363
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Thursday, February 22, 2024 ---------------------------------
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