- 4366 - CLOSEST SUPERNOVAE - examined by JWST. We can’t see light coming from the compact object itself, whether it’s a neutron star or a black hole. But, we do see radiation from the heated material drawn into the accretion disk around the compact object. And, since astronomers were able to track the changes in the light curve due to activity by the massive object, it amounted to watching its formation.
------------ 4366 - CLOSEST SUPERNOVAE - examined by JWST.
- In November of
1572, Tycho Brahe noticed a new star in the constellation Cassiopeia. It was
the first supernova to be observed in detail by Western astronomers and became
known as Tycho’s Supernova. Earlier supernovae had been observed by Chinese and
Japanese astronomers, but Tycho’s observations demonstrated to the Catholic
world that the stars were not constant and unchanging as Aristotle presumed.
-
- Just three
decades later, in 1604, Johannes Kepler watched a supernova in the
constellation Ophiuchus brighten and fade. There have been no observed
supernovae in the Milky Way since then.
-
- More than three
centuries passed since Galileo pointed his first telescopes to the
heavens. We launched telescopes into
space, landed on the Moon, and sent robotic probes to the outer solar system.
But there were no nearby supernovae to observe with our clever tools.
-
- Until February
1987, when a supernova appeared in the Large Magellanic Cloud. Known as “SN
1987a”, it reached a maximum apparent magnitude of about 3. It is the only
naked-eye supernova to occur within the era of modern astronomy.
-
- SN 1987a is right
in our backyard, only 168,000 light-years away. It has been studied over the
years by both land-based and space-based telescopes, and recently the James
Webb Space Telescope has taken a closer look. The results tell us much about
the rare supernova but also raise a few questions.
-
- Most prominent is
the bright equatorial ring of ionized gas. This ring was ejected from the star
for thousands of years before it exploded. It’s now heated by shockwaves from
the supernova. The equatorial ring girdles the hourglass shape of the fainter
outer rights that stem from the polar regions of the star. These structures
have been observed before by telescopes such as Hubble and Spitzer.
-
- JWST’s real power
is to peer into the center of SN 1987a. There it reveals a turbulent keyhole
structure where clumps of gas expand into space. Rich chemical interactions
have begun to occur in this region.
-
- JWST wasn’t able
to observe the ultimate jewel of the supernova, the remnant star. Supernovae
not only cast off new material into interstellar space, they also trigger the
collapse of the star’s core to become a neutron star or black hole. Based on
the scale of SN 1987a, a neutron star should have formed in its center.
However, the gas and dust of the inner keyhole region are too dense for JWST to
observe it.
-
- How a neutron star
forms, and how it interacts with surrounding gas and dust, is a mystery that
will require further study. We have observed the neutron stars of some
supernovae, but only from a much greater distance.
-
- Tycho’s supernova
was just 8,000 light-years from Earth, and Kepler’s about 20,000 light-years
distant. Unless Betelgeuse happens to explode in the near future, SN 1987a is
likely the closest new supernova we’ll be able to study for quite some time.
-
- The supernova, “SN
2022jli”, occurred when a massive star died in a fiery explosion, leaving
behind a compact object, a neutron star or a black hole. This dying star,
however, had a companion which was able to survive this violent event. The
periodic interactions between the compact object and its companion left
periodic signals in the data, which revealed that the supernova explosion had
indeed resulted in a compact object.
-
- When supernova SN
2022jli occurred in the nearby galaxy NGC 157 this stardeath event was
discovered in May, 2022. Astronomers
measurements and radiation showed something unusual, not like a “normal”
supernova.
-
- Their analysis
showed the supernova explosion ended up creating a massive compact object. No one has observed the process happen in
(almost) real-time. That makes the light curve a useful window on the creation
of either a neutron star or a black hole.
-
- In SN 2022jli’s
data we see a repeating sequence of brightening and fading. This is the first
time that repeated periodic oscillations, over many cycles, have been detected
in a supernova light curve.
-
- Supernovae occur
pretty frequently in the Universe. Astronomers study them and chart how their
brightness changes over time. After the initial explosion, the light it
generates fades out over some time. Usually, it’s a pretty smooth change in the
light curve. But, SN 2022jli didn’t fit the “normal” curve. Instead of fading
out smoothly, the brightness of light from the explosion oscillated in a
12-day-long period. They also detected
the motions of hydrogen gas and gamma-ray bursts in the region.
-
- The result of a
rapidly spinning neutron star (a pulsar) at its heart, surrounded by material
rushing out from the site of the explosion. SN 2022jli could have either a
neutron star or a black hole orbiting with a companion star.
-
- What story does
SN 2022jli’s strange light curve tell us about the creation of black holes or
neutron stars? The explosion was a fine
example of what astronomers call “Type II supernovae”. At the end of its life, a supermassive star
collapses and then explodes outward. The remaining core collapses further to
create one of two types of massive objects.
-
-
A neutron star is one. It’s what’s left over after the rapidly
collapsing core of the star crushes the remaining protons and neutrons of
matter into neutrons. It’s essentially a ball of neutrons. Most neutron stars
have about the mass of the Sun crushed inside themselves. But, they are small
compared to their progenitor stars. Most are maybe 20 kilometers across.
-
- Stellar-mass black
holes also come from the deaths of supermassive stars that were at least 20
times the mass of the Sun or more. The core collapses during the event, the
same as with a neutron star. But, the mass is so great that the event creates a
black hole, crushing all the leftover core material into a pinpoint of dense
matter.
-
- Like many massive
stars, the progenitor of SN 2022jli appears to have had at least one companion
star. It probably survived the supernova explosion. The outburst threw out huge
amounts of material, and the companion star interacted with it. That caused its
atmosphere to “puff up”.
-
- The newly created
compact object passes through the orbit of the star and sucks hydrogen gas away
from the star. That material funnels into an accretion disk around the compact
object. Those periodic episodes of matter theft from the star release lots of
energy, which gets picked up as regular changes of brightness in the light
curve measurements as well as the gamma-ray signals.
-
- Was it a neutron
star with tremendously strong magnetic fields and gravity, or a black hole with
gravity so strong nothing (not even light) could escape it? Determining that
requires additional observations and the capabilities of telescopes not yet
online, such as the “Extremely Large Telescope” due to begin operations in a
few years.
-
-
February 26, 2024
CLOSEST SUPERNOVAE - examined by JWST. 4366
-------------------------------------------------------------------------------------------------
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Sunday, February 25, 2024 ---------------------------------
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