- 4173 - WEBB - finds the earliest galaxies? James Webb telescope spots thousands of Milky Way lookalikes that 'shouldn't exist' swarming across the early universe. It has found more than 1,000 galaxies mysteriously resembling our own Milky Way hiding out in the early universe.
--------------------- 4173 - WEBB - finds the earliest galaxies?
- Shaped like warped
vinyls and sporting delicate spiral arms, the Milky Way look alikes were found
by JWST more than 10 billion years into the universe's past. This is during a period when violent galactic
mergers were thought to have made an abundance of such fragile galaxies
impossible.
-
- Yet the disk
galaxies are 10 times more common in the early universe than astronomers
previously thought. The strange discovery joins others made by the JWST that
point to a deepening mystery around how large galaxies, and with them the
potential for life, first bloomed in our universe.
-
- For over 30 years
it was thought that these disk galaxies were rare in the early universe due to
the common violent encounters that galaxies undergo. The fact that JWST finds so many is another
sign of the power of this instrument and that the structures of galaxies form
earlier in the universe, much earlier in fact, than anyone had anticipated.
-
- Most theories of
galaxy formation begin 1 billion to 2 billion years into the universe's life,
by which time the earliest clusters of stars were thought to have morphed into
dwarf galaxies. These dwarf galaxies subsequently began cannibalizing each
other, sparking a free-for-all of violent galactic mergers that after 10
billion years resulted in large galaxies like our own.
-
- The Milky Way is a
disk galaxy. With its spiral arms and squashed sombrero shape, it is one of the
most common types of galaxy in today's universe. However, during the universe's
early years, when the cosmos was more cramped and dwarf galaxies swarmed,
astronomers long-assumed that galaxies like our own would be quickly twisted
out of shape.
-
- Yet by using the JWST to peer from 9 billion
up to 13 billion years into the past, the astronomers discovered that, out of
the 3,956 galaxies they had spotted, 1,672 were disk galaxies like our own.
Many of these galaxies existed when the universe was just a few billion years
old.
-
- Using the Hubble
Space Telescope we thought that disk galaxies were almost non-existent until
the universe was about 6 billion years old.
These new JWST results push the time these Milky Way–like galaxies form
to almost the beginning of the universe.
-
- This implies that
most stars exist and form within these galaxies which is changing our complete
understanding of how galaxy formation occurs.
Based on our results astronomers must rethink our understanding of the
formation of the first galaxies and how galaxy evolution occurred over the past
10 billion years.
-
- Our own existence
in a disk galaxy means that astronomers usually assume they must have good
conditions for sparking life. If that’s the case, it’s possible that life could
have started earlier in the universe than first thought.
-
- A massive star
that exploded in the Pinwheel Galaxy in May appears to have unexpectedly lost
approximately one sun's worth of ejected mass during the final years of its
life before going supernova, new observations have shown.
-
- This star had
exploded in the nearby Pinwheel Galaxy (Messier 101), which is just 20 million
light-years away in the constellation of Ursa Major, the Great Bear. Cosmically
speaking, that's pretty close.
-
- Amateur
astronomers around the world started gazing at SN 2023ixf because the Pinwheel
in general is a popular galaxy to observe. However, haste is key when it comes to supernova
observations. Astronomers are keen to
understand exactly what is happening in the moments immediately after a star
goes supernova. Yet all too often, a supernova is spotted several days after
the explosion took place, so they don’t get to see its earliest stages.
-
- Considering how close,
relatively speaking, SN 2023ixf was to us and how early it was identified, it
was a prime candidate for close study.
Astronomers measured the supernova's light spectrum, and how that light
changed over the coming days and weeks. When plotted on a graph, this kind of
data forms a "light curve."
-
- This spectrum from
SN 2023ixf showed that it was a “type II supernova”, a category of supernova
explosion involving a star with more than eight times the mass of the sun. In
the case of SN 2023ixf, searches in archival images of the Pinwheel suggested
the exploded star may have had a mass
between 8 and 10 times that of our sun. The spectrum was also very red,
indicating the presence of lots of dust near the supernova that absorbed bluer
wavelengths but let redder wavelengths pass.
-
- Normally, a type II
supernova experiences what astronomers call a 'shock breakout' very early in
the supernova's evolution, as the blast wave expands outwards from the interior
of the star and breaks through the star's surface. Yet a bump in the light
curve from the usual flash of light stemming from this shock breakout was
missing. It didn’t turn up for several
days. Was this a supernova in slow motion.
-
- The delayed shock
breakout is direct evidence for the presence of dense material from recent mass
loss. New observations revealed a
significant and unexpected amount of mass loss, close to the mass of the sun,
in the final year prior to explosion.
-
- This unstable star
puffing off huge amounts of material from its surface. This creates a dusty
cloud of ejected stellar material all around the doomed star. The supernova
shock wave therefore not only has to break out through the star, blowing it
apart, but also has to pass through all this ejected material before it becomes
visible. This took several days for the
supernova in question.
-
- Massive stars
often shed mass. Betelgeuse star took from late 2019 and to early 2020, when it
belched out a cloud of matter with ten times the mass of Earth’s moon that
blocked some of Betelgeuse’s light, causing it to appear dim.
-
- However,
Betelgeuse isn’t ready to go supernova just yet, and by the time it does, the
ejected cloud will have moved far enough away from the star for the shock
breakout to be immediately visible. In the case of SN 2023ixf, the ejected
material was still very close to the star, meaning that it had only recently
been ejected, and astronomers were not expecting that.
-
- The only way to
understand how massive stars behave in the final years of their lives up to the
point of explosion is to discover supernovae when they are very young, and
preferably nearby, and then to study them across multiple wavelengths. Using both optical and millimeter telescopes
astronomers effectively turned SN 2023ixf into a time machine to reconstruct
what its progenitor star was doing up to the moment of its death.
-
- An evolved massive
star as being like an onion, with different layers. Each layer is made from a
different element, produced by sequential nuclear burning in the star's
respective layers as the stellar object ages and its core contracts and grows
hotter. The outermost layer is hydrogen, then you get to helium.
-
- Then, you go
through carbon, oxygen, neon and magnesium in succession until you reach all
the way to silicon in the core. That silicon is able to undergo nuclear fusion
reactions to form iron, and this is where nuclear fusion in a massive star’s
core stops because iron requires more energy to be put into the reaction than
comes out of it, which is not efficient for the star. Thus the core switches
off, the star collapses onto it and then rebounds and explodes outwards
-
- One possibility is
that the final stages of burning high-mass elements inside the star, such as
silicon (which is used up in the space of about a day), is disruptive, causing
pulses of energy that shudder through the star and lift material off its
surface.
-
-
October 1, 2023 WEBB -
finds the earliest galaxies?
4173
------------------------------------------------------------------------------------------
-------- Comments
appreciated and Pass it on to whomever is interested. ---
--- Some reviews are
at: -------------- http://jdetrick.blogspot.com -----
-- email feedback,
corrections, request for copies or Index of all reviews
--- to: ------
jamesdetrick@comcast.net
------ “Jim Detrick” -----------
--------------------- ---
Tuesday, October 3, 2023 ---------------------------------
No comments:
Post a Comment