- 4252 - SUPERNOVA - closest ever seen? - More than three centuries passed since Galileo pointed his first telescopes to the heavens. Astrophotography revolutionized our view of the heavens, as did radio astronomy. We launched telescopes into space, landed on the Moon, and sent robotic probes to the outer solar system.
-------------------------- 4252 - SUPERNOVA - closest ever seen?
- 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.
-
- There were no
nearby supernovae to observe with our clever new tools. Until February 1987,
when a supernova appeared in the Large Magellanic Cloud. Known as SN 1987a, it
reached a maximum apparent magnitude of
“3”. It is the only naked-eye supernova to occur within the era of
modern astronomy.
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- SN 1987a is 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 in
the image 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. But 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 triggerd 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.
-
- Space is full of
these extreme phenomena. The
“Tasmanian devil” may be one of the weirdest and rarest cosmic events ever
observed. Months after astronomers
witnessed the explosion of a distant star, they spotted something they have
never seen before: energetic signs of life releasing from the stellar corpse
about 1 billion light-years from Earth. The short, bright flares were just as powerful
as the original event that caused the star’s death.
-
- Astronomers named
the celestial object the “Tasmanian devil,” and they observed it exploding
repeatedly following its initial detection in September 2022. But the initial stellar explosion that
caused the star’s death wasn’t any typical supernova, an increasingly bright
star that explodes and ejects most of its mass before dying. Instead, it was a
rare type of explosion called a “luminous fast blue optical transient”, or LFBOT.
- The explosion
shines brightly in blue light, reaching the peak of brightness and fading within days, while
supernovas can take weeks or months to dim. The first LFBOT was discovered in
2018, and astronomers have been trying to determine the cause of the rare
cataclysmic events since.
-
- While LFBOTs are
unusual events, the Tasmanian devil is even stranger, causing astronomers to
question the processes behind the repetitive explosions. Instead of fading steadily as one would
expect, the source briefly brightened again and again, and again”.
-
- The findings about
the latest Tasmanian devil LFBOT discovery, officially labeled AT2022tsd and
observed with 15 telescopes around the globe.
LFBOTs emit more energy than an entire galaxy of hundreds of billions of
stars like the Sun. The mechanism behind this massive amount of energy is
currently unknown.
-
- After the initial
burst and fade, the extreme explosions just kept happening, occurring very
fast, over minutes, rather than weeks to months, as is the case for supernovae.
-
- Astronomers sift
through a half-million transients detected daily by the Zwicky Transient
Facility in California, which surveys the night sky. They continue to monitor the explosion as it
faded and reviewed the observations a few months later. The images showed
intense bright spikes of light that soon vanished.
-
- To better
understand the quick luminosity changes occurring in the Tasmanian devil, they
reached out to other researchers to compare observations from multiple
telescopes.
Altogether, the 15 observatories, including the high-speed
camera ULTRASPEC mounted on the 2.4-meter Thai National Telescope, tracked 14
irregular light pulses over 120 days, which is likely just a fraction of the
total number of flares released by the LFBOT.
-
- Some of the flares
only lasted tens of seconds, which to astronomers suggests that the underlying
cause is a stellar remnant formed by the initial explosion, either a dense
neutron star or a black hole.
-
- This pushes the
limits of physics because of its extreme energy production, but also because of
the short duration bursts. Light
travels at a finite speed. As such, how fast a source can burst and fade away
limits the size of a source, meaning that all this energy is being generated
from a relatively small source.
-
- If it’s a black
hole, the celestial object may be ejecting jets of material and launching them
across space at near the speed of light.
Another possibility is that the initial explosion was triggered by an
unconventional event, such as a star merging with a black hole, which could
present a completely different channel for cosmic cataclysms.
-
- Studying LFBOTs
could reveal more about the afterlife of a star, rather than just its life
cycle that ends with an explosion and a remnant. Because the corpse is not just sitting
there, it’s active and doing things that we can detect. We think these flares could be coming from
one of these newly formed corpses, which gives us a way to study their properties
when they’ve just been formed.
-
- Astronomers will
keep surveying the sky for LFBOTs to see how common they are and uncover more
of their secrets.
-
December 4, 2023
SUPERNOVA - closest ever seen? 4252
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