Birth of a Black Hole
Δημοσιεύτηκε στις 29 Νοε 2012
It
was one of the greatest mysteries in modern science: a series of brief
but extremely bright flashes of ultra-high energy light coming from
somewhere out in space. These gamma ray bursts were first spotted by spy
satellites in the 1960s. It took three decades and a revolution in
high-energy astronomy for scientists to figure out what they were.
Far
out in space, in the center of a seething cosmic maelstrom. Extreme
heat. High velocities. Atoms tear, and space literally buckles. Photons
fly out across the universe, energized to the limits found in nature.
Billions of years later, they enter the detectors of spacecraft
stationed above our atmosphere. Our ability to record them is part of a
new age of high-energy astronomy, and a new age of insights into nature
at its most extreme. What can we learn by witnessing the violent birth
of a black hole?
The outer limits of a black hole, call the event
horizon, is subject to what Albert Einstein called frame dragging, in
which space and time are pulled along on a path that leads into the
black hole. As gas, dust, stars or planets fall into the hole, they form
into a disk that spirals in with the flow of space time, reaching the
speed of light just as it hits the event horizon. The spinning motion of
this so-called "accretion disk" can channel some of the inflowing
matter out into a pair of high-energy beams, or jets.
How a jet
can form was shown in a supercomputer simulation of a short gamma ray
burst. It was based on a 40-millisecond long burst recorded by Swift on
May 9, 2005. It took five minutes for the afterglow to fade, but that
was enough for astronomers to capture crucial details. It had come from a
giant galaxy 2.6 billion light years away, filled with old stars.
Scientists
suspected that this was a case of two dead stars falling into a
catastrophic embrace. Orbiting each other, they moved ever closer,
gradually gaining speed. At the end of the line, they began tearing each
other apart, until they finally merged. NASA scientists simulated the
final 35 thousandths of a second, when a black hole forms.
Chaos
reigns. But the new structure becomes steadily more organized, and a
magnetic field takes on the character of a jet. Within less than a
second after the black hole is born, it launches a jet of particles to a
speed approaching light.
A similar chain of events, in the
death of a large star, is responsible for longer gamma ray bursts. Stars
resist gravity by generating photons that push outward on their
enormous mass. But the weight of a large star's core increases from the
accumulation of heavy elements produced in nuclear fusion. In time, its
outer layers cannot resist the inward pull... and the star collapses.
The crash produces a shock wave that races through the star and
obliterates it.
In the largest of these dying stars, known as
collapsars or hypernovae, a black hole forms in the collapse. Matter
flowing in forms a disk. Charged particles create magnetic fields that
twist off this disk, sending a portion out in high-speed jets.
Simulations
show that the jet is powerful enough to plow its way through the star.
In so doing, it may help trigger the explosion. The birth of a black
hole does not simply light up the universe. It is a crucial event in the
spread of heavy elements that seed the birth of new solar systems and
planets.
But the black hole birth cries that we can now
register with a fleet of high-energy telescopes are part of wider
response to gravity's convulsive power.
was one of the greatest mysteries in modern science: a series of brief
but extremely bright flashes of ultra-high energy light coming from
somewhere out in space. These gamma ray bursts were first spotted by spy
satellites in the 1960s. It took three decades and a revolution in
high-energy astronomy for scientists to figure out what they were.
Far
out in space, in the center of a seething cosmic maelstrom. Extreme
heat. High velocities. Atoms tear, and space literally buckles. Photons
fly out across the universe, energized to the limits found in nature.
Billions of years later, they enter the detectors of spacecraft
stationed above our atmosphere. Our ability to record them is part of a
new age of high-energy astronomy, and a new age of insights into nature
at its most extreme. What can we learn by witnessing the violent birth
of a black hole?
The outer limits of a black hole, call the event
horizon, is subject to what Albert Einstein called frame dragging, in
which space and time are pulled along on a path that leads into the
black hole. As gas, dust, stars or planets fall into the hole, they form
into a disk that spirals in with the flow of space time, reaching the
speed of light just as it hits the event horizon. The spinning motion of
this so-called "accretion disk" can channel some of the inflowing
matter out into a pair of high-energy beams, or jets.
How a jet
can form was shown in a supercomputer simulation of a short gamma ray
burst. It was based on a 40-millisecond long burst recorded by Swift on
May 9, 2005. It took five minutes for the afterglow to fade, but that
was enough for astronomers to capture crucial details. It had come from a
giant galaxy 2.6 billion light years away, filled with old stars.
Scientists
suspected that this was a case of two dead stars falling into a
catastrophic embrace. Orbiting each other, they moved ever closer,
gradually gaining speed. At the end of the line, they began tearing each
other apart, until they finally merged. NASA scientists simulated the
final 35 thousandths of a second, when a black hole forms.
Chaos
reigns. But the new structure becomes steadily more organized, and a
magnetic field takes on the character of a jet. Within less than a
second after the black hole is born, it launches a jet of particles to a
speed approaching light.
A similar chain of events, in the
death of a large star, is responsible for longer gamma ray bursts. Stars
resist gravity by generating photons that push outward on their
enormous mass. But the weight of a large star's core increases from the
accumulation of heavy elements produced in nuclear fusion. In time, its
outer layers cannot resist the inward pull... and the star collapses.
The crash produces a shock wave that races through the star and
obliterates it.
In the largest of these dying stars, known as
collapsars or hypernovae, a black hole forms in the collapse. Matter
flowing in forms a disk. Charged particles create magnetic fields that
twist off this disk, sending a portion out in high-speed jets.
Simulations
show that the jet is powerful enough to plow its way through the star.
In so doing, it may help trigger the explosion. The birth of a black
hole does not simply light up the universe. It is a crucial event in the
spread of heavy elements that seed the birth of new solar systems and
planets.
But the black hole birth cries that we can now
register with a fleet of high-energy telescopes are part of wider
response to gravity's convulsive power.
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