- 4428 - GAMMA RAY BURSTS - from stars that collide? - Two neutron stars begin to merge blasting jets of high-speed particles creating short gamma-ray bursts. These are the most powerful events in the known universe. Gamma-ray bursts are short-lived outbursts of the highest-energy light. They can erupt with a quintillion (a 10 followed by 18 zeros) times the luminosity of our sun. They are now thought to announce the births of new black holes, they were discovered by accident.
------------------------- 4428 - GAMMA RAY BURSTS - from stars that collide?
- The backstory takes us to 1963, when the
U.S. Air Force launched the Vela satellites to detect gamma rays from banned
nuclear weapons tests. The United States had just signed a treaty with the
United Kingdom and the Soviet Union to prohibit tests within Earth's
atmosphere, and the Vela satellites ensured all parties' compliance. Instead,
the satellites stumbled upon 16 gamma-ray events.
-
- By 1973, scientists could rule out that
both Earth and the sun were the sources of these brilliant eruptions. That's
when astronomers at Los Alamos National Laboratory published the first paper
announcing these bursts originate beyond our solar system.
-
- Scientists at NASA's Goddard Space Flight
Center quickly confirmed the results through an X-ray detector on the IMP 6
satellite. It would take another two decades and contributions from the Italian
Space Agency's BeppoSax and NASA's Compton Gamma-Ray Observatory to show that
these outbursts occur far beyond our Milky Way galaxy, are evenly distributed
across the sky, and are extraordinarily powerful. The closest GRB on record
occurred more than 100 million light-years away.
-
- Though discovered by chance, GRBs have
proven invaluable for today's researchers. These flashes of light are rich with
insight on phenomena like the end of life of very massive stars or the
formation of black holes in distant galaxies.
-
- In 2017, GRBs were first linked to
gravitational waves, ripples in the fabric of space-time, steering us toward a
better understanding of the how these events work. Astronomers separate GRBs into two main
classes: short (where the initial burst of gamma rays lasts less than two
seconds) and long events (lasting two seconds or longer).
-
- Shorter bursts also produce fewer gamma
rays overall, which lead researchers to hypothesize that the two classes
originated from different systems.
Astronomers now associate short bursts with the collision of either two
neutron stars or a neutron star and a black hole, resulting in a black hole and
a short-lived explosion.
-
- Short GRBs are sometimes followed by
kilonovae, light produced by the radioactive decay of chemical elements. That
decay generates even heavier elements, like gold, silver, and platinum.
-
- Long bursts are linked to the explosive
deaths of massive stars. When a high-mass star runs out of nuclear fuel, its
core collapses and then rebounds, driving a shock wave outward through the
star. Astronomers see this explosion as a supernova. The core may form a either
a neutron star or a black hole.
-
- In both classes, the newly born black hole
beams jets in opposite directions. The jets, made of particles accelerated to
near the speed of light, pierce through and eventually interact with the
surrounding material, emitting gamma rays when they do.
-
- In August 2020, NASA's Fermi Gamma-ray
Space Telescope tracked down a second-long burst named “GRB 200826A”, more than
6 billion light-years away. It should have fallen within the short-burst class,
triggered by mergers of compact objects.
-
- However, other characteristics of this
event—like the supernova it created—suggested it originated from the collapse
of a massive star. Astronomers think this burst may have fizzled out before it
could reach the duration typical of long bursts.
-
- Fermi and NASA's Neil Gehrels Swift
Observatory captured its opposite number, “GRB 211211A” in December 2021.
Located a billion light-years away, the burst lasted for about a minute. While
this makes it a long GRB, it was followed by a kilonova, which suggests it was
triggered by a merger. Some researchers attribute this burst's oddities to a
neutron star merging with a black hole partner.
-
- As astronomers discover more bursts lasting
several hours, there may still be a new class in the making: “Ultra-long GRBs”.
The energy created by the death of a high-mass star likely can't sustain a
burst for this long, so scientists must look to different origins.
-
- Some think ultra-long bursts occur from
newborn magnetars—neutron stars with rapid rotation rates and magnetic fields a
thousand times stronger than average. Others say this new class calls for the
power of the universe's largest stellar residents, “blue supergiants”.
Researchers continue to explore ultra-long GRBs.
-
- GRB afterglows occur when material in the
jets interact with surrounding gas.
Afterglows emit radio, infrared, optical, UV, X-ray, as well as
gamma-ray light, which provides more data about the original burst. Afterglows
also linger for hours to days (or even years) longer than their initial
explosion, creating more opportunities for discovery.
-
- Studying afterglows became key to deducing
the driving forces behind different bursts. In long bursts, as the afterglow
dims, scientists eventually see the source brighten again as the underlying
supernova becomes detectable.
-
- Although light is the universe's fastest
traveler, it can't reach us instantaneously. By the time we detect a burst,
millions to billions of years may have passed, allowing us to probe some of the
early universe through distant afterglows.
Our understanding of GRBs is far from complete. Each new discovery adds
new facets to scientists' gamma-ray burst models.
-
- Fermi and Swift discovered one of these
revolutionary events in 2022 with GRB 221009A, a burst so bright it temporarily
blinded most space-based gamma-ray instruments. A GRB of this magnitude is
predicted to occur once every 10,000 years, making it likely the
highest-luminosity event witnessed by human civilization. Astronomers
accordingly dubbed it the brightest of all time—or the “BOAT”.
-
- This is one of the nearest long burst ever
seen at the time of its discovery, offering scientists a closer look at the inner
workings of not only GRBs, but also the structure of the Milky Way. By peering
into the BOAT, they've discovered radio waves missing in other models and
traced X-ray reflections to map out our galaxy's hidden dust clouds.
-
- GRBs also connect us to one of the
universe's most sought-after messengers. Gravitational waves are invisible
distortions of space-time, born from cataclysmic events like neutron-star
collisions. Think of space-time as the universe's all-encompassing blanket,
with gravitational waves as ripples wafting through the material.
-
- In 2017, Fermi spotted the gamma-ray flash
of a neutron-star merger just 1.7 seconds after gravitational waves were
detected from the same source. After traveling 130 million light-years, the
gravitational waves reached Earth narrowly before the gamma rays, proving
gravitational waves travel at the speed of light.
-
- Scientists had never detected light and
gravitational waves' joint journey all the way to Earth. These messengers
combined paint a more vivid picture of merging neutron stars.
-
-
April 11, 2023 GAMMA
RAY BURSTS - from
stars that collide? 4428
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2024
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