- 4287 - BLACKHOLES - in the early Universe? - Scientists have discovered gravitational waves stemming from a black hole merger event that suggest the resultant black hole settled into a stable, spherical shape. These waves also reveal the combo black hole may be much larger than previously thought.
------------------------- 4287 - BLACKHOLES - in the early Universe?
- When initially
detected on May 21, 2019, the gravitational wave event known as “GW190521” was
believed to have come from a merger between two black holes, one with a mass
equivalent to just over 85 suns and the other with a mass equivalent to about
66 suns. The merger created an
approximately 142 solar mass daughter black hole.
-
- Newly studied
spacetime vibrations from the merger-created black hole, rippling outward as
the void resolved into a proper spherical shape, seem to suggest it's more
massive than initially predicted. Rather than possess 142 solar masses,
calculations say it should have a mass equal to 250 times that of the sun.
-
- General relativity
theory predicts that objects with mass warp the very fabric of space and time,
united as a single, four-dimensional entity called "spacetime”",
and that "gravity" as we perceive it arises from the curvature
itself.
-
- Just as a bowling
ball placed on a stretched rubber sheet causes a more extreme "dent"
than a tennis ball would, a black hole causes more curvature in spacetime than
a star does, and a star causes more curvature than a planet does. In fact, a
black hole, in general relativity, is a point of matter so dense it causes
curvature of spacetime so extreme that, at a boundary called the event horizon,
not even light is fast enough to escape the inward dent.
-
- This isn't the
only revolutionary prediction of general relativity, however. Einstein also
predicted that when objects accelerate, they should set the very fabric of
spacetime ringing with ripples called “gravitational waves”. The more massive the objects involved, the
more extreme the phenomenon is. This means when dense bodies like black holes
spiral around one another, constantly accelerating due to their circular motion,
spacetime rings around them like a struck bell, humming with gravitational waves.
-
- These ripples in
spacetime carry away angular momentum from the spiraling black holes, and that,
in turn, causes the black holes' mutual orbits to tighten, drawing them
together and increasing the frequency of the gravitational waves emitted.
Spiraling closer and closer, the black holes finally merge, creating a daughter
black hole and sending a high-frequency "chirp" of gravitational
waves echoing out through the cosmos.
-
- But there was one
thing Einstein got wrong about gravitational waves. The great physicist
believed that these ripples in spacetime would be so faint that they would
never be detected here on Earth after traveling across the universe for
millions, or even billions, of light years.
-
- In September,
2015, the twin detectors of the Laser Interferometer Gravitational-Wave
Observatory (LIGO) based in Washington and Louisiana showed Einstein was
incorrect. They detected GW150914, gravitational waves associated with merging
black holes located 1.3 billion light-years away.
-
- The gravitational
wave signal was detected as a change in the length of one of LIGO's 2.5
miles long laser arms, equivalent to a
thousandth the width of a proton.
-
- Since then, LIGO
and its fellow gravitational wave detectors, Virgo in Italy and KAGRA in Japan,
have detected many more such events,
reaching the point at which they are detecting one gravitational wave event
each week. Although, even among these gravitational wave detections, GW190521
stands out.
-
- The merging
frequency of the two black holes behind the GW190521 signal, which are located
as far away as 8.8 billion light-years from Earth, was so low it was only
during the final two orbits of the black holes that the frequency became high
enough to reach the sensitivity limits of LIGO and Virgo.
-
- The instant the
black holes collided, the resultant black hole was created with a lopsided
shape. Black holes are only stable when they have a spherical shape, meaning
that within milliseconds of the merger, the daughter black hole would have to
assume the shape of a sphere.
-
- Just as the shape
of a bell determines the frequency at which it rings, this new black hole
changed shape and stabilized, the frequencies of the gravitational waves it
rang out were shifted. These so-called "ring down" gravitational
waves contained information about the mass of the daughter black hole and also
the rate at which it is spinning.
-
- The ring-down
gravitational waves from such a merger offer scientists an alternative way to
measure the properties of merging black holes, in contrast to the traditional
method of using the gravitational waves created during the spiraling process.
-
- Two separate
“ring-down frequencies” in the gravitational wave signal when considered
together, give the created black hole a mass of 250 solar masses. That means
it's considerably more massive than estimated by using the spiraling
gravitational waves.
-
-The James Webb Space Telescope (JWST) has spotted the oldest
black hole ever seen, an ancient monster with the mass of 1.6 million suns
lurking 13 billion years in the universe's past. They spotted the supermassive black hole at
the center of the infant galaxy GN-z11 just 440 million years after the
universe began.
-
- How the cosmic
whirlpools ballooned in scale so rapidly after the universe began isn't clear.
But looking for an answer could help explain how today's supermassive black
holes, which anchor entire galaxies including our Milky Way, grew to such
mind-boggling sizes.
-
- Black holes in the
early universe can't grow quietly and gently as many black holes do in the
local present-day universe. Closer to
the present-day, astronomers believe black holes are born from the collapse of
giant stars. They grow by ceaselessly gorging on gas, dust, stars and other
black holes. As they feast, friction causes the material spiraling into the
black holes to heat up, and they emit light that can be detected by telescopes
turning them into “active galactic nuclei” (AGN).
-
- The most extreme
AGN are “quasars”, supermassive black holes that are billions of times heavier
than the sun and shed their gaseous cocoons with light blasts trillions of
times more luminous than the brightest stars.
-
- Because light
travels at a fixed speed through the vacuum of space, the deeper that
scientists look into the universe, the more remote light they intercept and the
further back in time they see.
-
- To spot the black
hole the astronomers scanned the sky with two infrared cameras, the JWST's
Mid-Infrared Instrument (MIRI) and Near Infrared Camera, and used the cameras' built-in spectrographs
to break down the light into its component frequencies.
-
- By deconstructing
these faint glimmers from the universe's earliest years, they found an
unexpected spike among the frequencies contained within the light. This was a key sign that the hot material
around a black hole was beaming out faint traces of light across the universe.
-
- The most popular
explanations for how these early black holes grew so fast are that they formed
from the sudden collapse of giant gas clouds or that they came from many
mergers between clumps of stars and black holes.
-
- Astronomers
haven't ruled out that some of these black holes could have been seeded by
hypothesized "primordial" black holes, thought to be created moments
after and in some theories even before
the universe began.
-
- You need it to be
a pristine cloud, yet to be enriched by heavy elements made by the first stars,
and one that is fairly massive, from 10,000 to up to a million solar masses
-
- To prevent such a
cloud from cooling too quickly and collapsing into massive stars first, it must
also be beamed with ultraviolet light, likely from a nearby galaxy or black
hole.
-
-
December 27, 2023
BLACKHOLES - in
the early Universe? 4279
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