- 4493 - SUPERNOVAE EXPLOSIONS - produce the heavier elements? - A recent study investigated one long gamma ray burst in particular, GRB 221009. This has been dubbed the BOAT, “the brightest of all time”. This GRB was picked up as a pulse of intense radiation sweeping through the solar system on October 9, 2022.
------------------------ 4493 - SUPERNOVAE EXPLOSIONS - produce the heavier elements?
- After its "birth" in the Big
Bang, the “universe” consisted mainly of hydrogen and a few helium atoms. These
are the lightest elements in the periodic table. More-or-less all elements
heavier than helium were produced in the 13.8 billion years between the Big
Bang and the present day.
-
- Stars have produced many of these heavier
elements through the process of nuclear fusion. However, this process only
makes elements as heavy as iron. The creation of any heavier elements would
consume energy instead of releasing it.
-
- In order to explain the presence of these
heavier elements today, it's necessary to find phenomena that can produce them.
One type of event that fits the bill is a gamma-ray burst (GRB)which are the
most powerful class of explosion in the universe. These can erupt at a
quintillion (10 followed by 18 zeros) times the luminosity of our sun, and are
thought to be caused by several types of events.
-
- GRBs can be subdivided into two categories:
long bursts and short bursts. Long GRBs are associated with the deaths of
massive and fast-rotating stars. According to this theory, the fast rotation
beams material ejected during the collapse of a massive star into narrow jets
that move at extremely fast speeds.
-
- The short bursts last only a few seconds.
They are thought to be caused by the collision of two neutron stars which are
compact and dense "dead" stars. In August, 2017, an important event
helped support this theory. Ligo and Virgo, two gravitational wave detectors in
the US, discovered a signal that seemed to be coming from two neutron stars
moving in for a collision.
-
- A few seconds later, a short gamma-ray
burst, known as “GRB 100817A”, was detected coming from the same direction in
the sky. For a few weeks, virtually every telescope on the planet was pointing
at this event in an unprecedented effort to study its aftermath.
-
- The observations revealed a kilonova at the
location of GRB 170817A. A “kilonova” is a fainter cousin of a supernova
explosion. More interestingly, there was evidence that many heavy elements were
produced during the explosion. This kilonova seemed to produce two different
categories of debris, or ejecta. One was composed primarily of light elements,
while another consisted of heavy elements.
-
- Nuclear fusion can only feasibly produce
elements as heavy as iron in the periodic table. But there's another process
which could explain how the kilonova was able to produce even heavier
ones. Rapid neutron-capture process, or
r-process, is where the nuclei (or cores) of heavier elements such as iron
capture many neutron particles in a short time.
-
- The kilonova can then rapidly grow in mass,
yielding much heavier elements. For r-process to work, however, you need the
right conditions: high density, high temperature, and a large number of
available free neutrons. Gamma ray bursts happen to provide these necessary
conditions.
-
- However, mergers of two neutron stars, like
the one that caused the kilonova GRB 170817A, are very rare events. In fact,
they may be so rare as to make them an unlikely source for the abundant heavy
elements we have in the universe. But what of long GRBs?
-
- The “BOAT” sparked a similar astronomical
observation campaign as the kilonova. This GRB was 10 times more energetic than
the previous record holder, and so close to us that its influence on the
Earth's atmosphere was measurable on the ground and comparable to a major solar
storm.
-
- Among the telescopes studying the aftermath
of the BOAT was the James Webb Space Telescope (JWST). It observed the GRB
about six months after it exploded, so as not to be blinded by the afterglow of
the initial burst. The data JWST collected showed that, despite the event's
extraordinary brightness, it was caused by a merely average supernova
explosion.
-
- Previous observations of other long GRBs
indicated that there is no correlation between the brightness of the GRB and
the size of the supernova explosion associated with it. The BOAT seems no
exception.
-
- The JWST team also inferred the number of
heavy elements produced during the BOAT explosion. They found no indication of
elements produced by the r-process. This is surprising as, theoretically, the
brightness of a long GRB is thought to be associated with the conditions in its
core, most likely a black hole. For very bright events, especially one as
extreme as the BOAT, the conditions should be right for the r-process to occur.
-
- These findings suggest that gamma ray bursts
may not be the hoped-for crucial source of the universe's heavy elements.
Instead, there must be a source or sources still out there.
-
-
June 6, 2024 SUPERNOVAE EXPLOSIONS
- produce the heavier elements? 4493
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