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Cosmic Journeys: The Largest Black Holes in the Universe
Poziom:
Temat: Nauka i technologia
We've never seen them directly,
yet we know they are there,
Lurking within dense star clusters,
Or wandering the dust lanes of the galaxy,
Where they prey on stars,
Or swallow planets whole.
Our Milky Way may harbor millions of these
black holes,
the ultra dense remnants of dead stars.
But now, in the universe far beyond our galaxy,
there's evidence of something even more ominous,
A breed of black holes that have reached incomprehensible
size and destructive power.
It has taken a new era in astronomy to find
them.
High-tech instruments in space tuned to sense
high-energy forms of light - x-rays and gamma
rays - that are invisible to our eyes.
New precision telescopes equipped with technologies
that allow them to cancel out the blurring
effects of the atmosphere,
and see to the far reaches of the universe.
Peering into distant galaxies, astronomers
are now finding evidence that space and time
can be shattered by eruptions so vast they
boggle the mind.
We are just beginning to understand the impact
these outbursts have had on the universe around
us.
That understanding recently took a leap forward.
A team operating at the Subaru Observatory
atop Hawaii's Mauna Kea volcano looked out
to one of the deepest reaches of the universe,
And captured a beam of light that had taken
nearly 13 billion years to reach us.
It was a messenger from a time not long after
the universe was born.
They focused on an object known as a quasar,
short for "quasi-stellar radio source."
It offered a stunning surprise,
A tiny region in its center is so bright that
astronomers believe it's light is coming from
a single object at least a billion times the
mass of our sun.
Inside this brilliant beacon, space suddenly
turns dark,
as it's literally swallowed by a giant black
hole.
As strange as they may seem, even huge black
holes like these are thought to be products
of the familiar universe of stars and gravity.
They get their start in rare types of large
stars, at least ten times the mass of our
sun.
These giants burn hot and fast, and die young.
The star is a cosmic pressure-cooker. In its
core, the crush of gravity produces such intense
heat that atoms are stripped and rearranged.
Lighter elements like hydrogen and helium
fuse together to form heavier ones like calcium,
oxygen, silicon, and finally iron.
When enough iron accumulates in the core of
the star, it begins to collapse under its
own weight.
That can send a shock wave racing outward,
Literally blowing the star apart:
a supernova.
At the moment the star dies, if enough matter
falls into its core, it collapses to a point,
forming a black hole.
Intense gravitational forces surround that
point with a dark sphere, the event horizon,
beyond which nothing, not even light, can
escape.
That's how an average-size black hole forms.
What about a monster the size of the Subaru
quasar?
Recent discoveries about the rapid rise of
these giant black holes have led theorists
to rethink their view of cosmic history.
Back in 1995, the Hubble Space Telescope was
enlisted to begin filling in the details of
that history.
Astronomers selected tiny regions in the sky,
between the stars,
Looking North, South, And south again.
For days at a time, they focused Hubble's
gaze on tiny patches of sky to examine the
deepest regions of the universe.
These Deep Field images offer incredibly clear
views of the cosmos in its infancy.
What drew astronomers' attention were the
tiniest galaxies, covering only a few pixels
on Hubble's detector.
Most of them do not have the grand spiral
or elliptical shapes of the large galaxies
we see closer to us today.
Instead, they are irregular, scrappy collections
of stars.
The Hubble Deep Field confirmed the idea that
the universe must have evolved in a series
of building blocks,
with small galaxies gradually merging and
assembling into larger ones.
You can see evidence of this pattern simply
by looking out into the universe.
Many galaxies are gyrating around one another.
Some are crashing together,
others ripping each other apart.
Gravity calls the tune as these galaxies draw
together, exchange stars and gas,
and, over time, merge to form larger composite
galaxies.
Lately, though, this picture of a universe
taking shape from the ground up has gotten
a lot more complicated.
The
quick appearance of giant black holes and
galaxies in the early universe is at odds
with the gradual way matter builds up of matter
in most galaxies.
They likely had their beginnings in the first
generations of stars that literally burst
onto the cosmic scene, in a time of incredible
turbulence.
These stars were born in knots that developed
in the diffuse gas of the early universe.
Gravity drew these knots together. In the
densest regions, stars were born in waves.
Many of them gave birth to black holes.
Within a relatively short time by cosmic standards,
the earliest black holes swallowed more and
more matter, growing to monumental proportions,
becoming quasars.
These quasars, in turn, were fed by the collapse
of matter on a much larger scale.
This computer simulation recreates a region
in the early universe that measured over a
hundred million light years on a side.
It shows what took place in the first one
billion years of cosmic history.
This virtual universe is set in motion by
equations describing the properties of gas,
the energy released in star birth, and the
outward motion of space and time.
The result: an intricate cosmic web, with
gravity drawing matter into filaments and
knots,
as if you're looking down through a vast tangle
of interconnected spider webs.
Inside the most dense regions is where the
largest galaxies, and black holes, grew.
Here, circles indicate the appearance of black
holes deep in the data.
As they bulk up, by eating up their surroundings,
the circles grow larger.
A few, in the largest galaxies, reach ultra
massive proportions, billions of times the
mass of our sun.
This is the scene in one of those dense intersections.
Thousands of galaxies, and gigantic clouds
of gas, spiral inward.
A large galaxy emerges in the center, and
at its center, a giant black hole forcefed
by gravity.
The orbiting Chandra X-Ray Observatory was
dispatched to look into distant galaxies for
black holes on a growth spurt.
Those that swallow gas and stars glow hotly
in X-ray light.
Chandra found them. It even spotted some in
pairs, black hole companions entwined in a
dance of death.
When the music ends, the pair swallows each
other!
That moment must be fast approaching for the
largest black hole detected in the universe
to date. It's a quasar called OJ-287.
Flareups in the surrounding region suggest
to astrophysicists that another black hole
is flying around it.
This giant's gravitational hold on its companion
has led astronomers to estimate it's mass
at a whopping 18 billion solar masses.
A monster this large and ferocious vents its
rage on the surrounding universe, and radically
changes it.
Just look at MS0735. Two and a half billion
light years away, it appears in visible light
to be a typical galaxy cluster.
But in X-ray light, it's enveloped in a cloud
of hot gas.
Hollowed out of this cloud are two immense
cavities up to 600,000 light years across.
Now, add in a radio image of the cluster,
and you can see two concentrated streams of
matter pushing out from the center.
That's a give-away that the cavities were
formed by an eruption in the core of the giant
central galaxy.
Two jets, shooting out of the galaxy, have
launched blast waves that have plowed through
the gas between the galaxies.
How much energy must that take? That of several
billion supernovas, according to one calculation.
That makes this the largest single eruption
recorded since the big bang.
Its source: a black hole that may weigh around
10 billion solar masses.
But how does a black hole, a creature famous
for hiding in the dark, emit this much energy?
Think of a black hole as the eye of a cosmic
hurricane, kept rotating by all the stars,
gas, and other black holes that happen to
fall into it.
As this matter flows in,
It forms a spinning donut-like feature called
an accretion disk, which works like a dynamo.
The spinning motion of that disk generates
magnetic fields that twist around and channel
some of the inflowing matter outwards into
a pair of high-energy beams, or jets.
How much energy depends upon the black hole's
gravity and how much matter has already crashed
through its event horizon.
Is this just another frightening spectacle
of Nature? Or is it part of a more profound
process at work?
Black hole jets have been seen all around
the universe, including in our own cosmic
neighborhood.
This is Centaurus A, also known as the "hamburger
galaxy."
In X-rays, you can see a jet erupting from
the center.
Peering through the dense dust lanes that
dominate our line of sight, astronomers have
come to believe that it's actually two galaxies
in the act of colliding.
Then there's the famous M87 galaxy, at the
center of the Virgo cluster of galaxies, around
50 million light years away.
Astronomers have been intensely studying the
four billion solar mass black hole that lurks
in its heart.
They found that in the tiny central region,
the gas is whipped by gravity to orbital speeds
of millions of kilometers per hour.
That's powering a pair of high-powered jets
that are plowing into the larger galaxy cluster.
The largest black holes in the universe probably
rose in the age of quasars, between 10 and
12 billion years ago.
By releasing energy in the form of jets, they
heated up the surrounding region.
This prevented gas from collapsing into the
center from the surrounding region, and allowed
smaller galaxies on the periphery to form
and grow.
But the monsters' impact did not stop there.
This Chandra image of the Hydra A galaxy cluster
shows the same immense hot cavities, glowing
in X-ray light,,
And a jet blasting out of its central galaxy.
Gas along the edge of the jet contains high
levels of iron and other metals probably from
supernova explosions in the center.
By pushing these metals into regions beyond,
a black hole seeds the universe with the elements
needed to form stars, planets, and solar systems
like ours.
Those smaller galaxies then begin to seed
their own environments.
This computer simulation shows the fate of
gas in the merger of two galaxies with black
holes embedded in their cores.
As the two pass by each other by, the pull
of gravity disrupts their spiral shapes, forcing
huge volumes of gas into their cores.
As these black holes continue to feed, they
emit a series of powerful shock waves that
push much of the loose gas beyond their boundaries.
In the final steps of this ballet, the two
black holes merge, emitting one final blast.
Our Earth, our star, the Sun,
our Solar System, and ourselves,
we all seem to be the beneficiaries of these
far-away monsters.
But equally amazing is the role these largest
black holes play in the great cosmic struggle
between gravity and energy.
