- 4098 - PLANETARY NEBULAE - at center of Milkyway? Astronomers know a great deal about planetary nebulas, but an arrangement of such clouds in the galactic bulge at the center of our Milky Way galaxy has still been a puzzle since its discovery 10 years ago, 2013.
------------ 4098 - PLANETARY NEBULAE - at center of Milkyway?
- A mysterious alignment
of stellar "ghosts" from dead stars haunts the heart of the Milky
Way. These cosmic specters exist in the
form of planetary nebulas, clouds of gas that are expelled by dying stars at
the end of their lives. These can resemble butterflies or hourglasses with the
smoldering remains of the star at their heart.
( 4099 - MILKYWAY
GALAXY - gas clouds at the center? )
-
- The sun, when it runs
out of fuel for nuclear fusion at its core and after it has swelled out as a
red giant and swallowed the inner planets in around 5 billion years, will leave
similar gaseous remains around a white dwarf star.
-
- Planetary nebulas offer
us a window into the heart of our galaxy and this insight deepens our
understanding of the dynamics and evolution of the Milky Way's bulge
region. Studying 136 planetary nebulas
in the thickest part of the Milky Way, the galactic bulge, with the Very Large
Telescope (VLT), astronomers discovered that each is unrelated and comes from
different stars, which died at different times and spent their lives in
different locations.
-
- The shapes of these
planetary nebulas line up in the sky in the same way. They are also aligned almost parallel to the
plane of the Milky Way. What wasn't
known until now was the fact that this alignment is only present in the
planetary nebulas that have a close stellar companion. In these cases, the
companion stars orbit the stellar remnant at the heart of the planetary nebulas
at a distance closer than our solar system's innermost planet Mercury is to the
sun.
-
- The alignment is absent
in planetary nebulas that lack such a companion star, and this implies that the
alignment could be created as a result of the rapid orbital motion of the
companion star, which may even end up orbiting inside the remains of the main
star. The observed alignment of the planetary nebulas may also reveal that
close binary systems form with their orbits inclined in the same plane.
-
- The formation of stars
in the bulge of our galaxy is a complex process that involves factors such as
gravity, turbulence, and magnetic fields.
-
- Nebula is a Latin word meaning
"cloud", it refers to any
celestial object which appears cloud-like when viewed through a telescope. When telescopes weren’t as powerful as they
are today, this term encompassed galaxies such as our neighbour Andromeda,
which was often referred to as the "Andromeda nebula".
-
- However, with the
benefit of modern telescopes we know that galaxies aren’t cloud-like at all,
but made up of billions of stars. This means astronomers now reserve the word
nebula for genuine clouds of gas and dust located inside our own galaxy.
-
- Nebula are often found
in the space between stars, known as the interstellar medium. On average, this
region contains only one atom per cubic centimeter. However, in certain places
the density can be significantly higher than this, high enough to become visible through a
telescope.
-
- The result is a nebula,
and they are among the most spectacular sights in astronomy. Many of the most
iconic Hubble telescope images, such as the "Pillars of Creation",
are images of nebula.
-
- There are several
different types of nebula, depending on how they form and their composition.
Most nebula are primarily made of gas, which is able to glow with its own
light, creating the colorful displays .
-
- But other nebula,
called "dark nebula", are much
dustier in their composition, and rather than glowing this dust has the effect
of blocking the light from more distant objects beyond it.
-
- A “diffuse nebula” with
ongoing star formation, the gas here is hot enough to glow with its own
light. Another type of diffuse nebula,
a “reflection nebula” doesn’t emit its own light, but scatters light from
embedded stars. This is composed of
expanding gas that was blown off by a star as it collapsed to a white dwarf.
-
- Nebula play a key role
in the life cycle of stars, both at their birth and death. Stars are born in
dense clumps of gas, dust, and other material inside diffuse emission nebulae,
also frequently referred to as "stellar nurseries".
-
- The principal force at
work here is gravity, which causes the tenuous interstellar medium to condense
into a nebula, and gravity that causes clumps inside the nebula to collapse
down into stars.
-
- At the other end of a
star’s life, we encounter a different type of emission nebula. Stars like the
sun end their lives as highly compact white dwarfs, but as they shrink down
into this phase they release clouds of gas which form a so-called
"planetary nebula". This is a rather misleading name, because such
nebula have nothing to do with planets. Unlike diffuse emission nebula, these
have a more clearly defined appearance, usually circular in shape.
-
- Not all stars end their
days in the relative serenity of a planetary nebula. A star that’s much more
massive than the sun will eventually explode as a supernova, and the debris
flung out from that explosion forms yet another kind of nebula called a
supernova remnant. The most famous of these is the Crab Nebula, which is all
that remains of a spectacular supernova that was observed by Chinese
astronomers in 1054.
-
- The visible light
emitted by stars forming in and around a nebula can be blocked by the dense
cosmic clouds of gas and dust that make up a nebula. Therefore, scientists must
look to other wavelengths of light that are emitted from the nebula, such as
infrared radiation.
-
- Infrared cameras
onboard the JWST have relieved some of the most detailed images of nebulae,
such as the Southern Ring planetary nebula. The Southern Ring nebula, NGC 3132,
is around 2,500 light-years away from Earth and home to a dying star at its
core.
-
- Using its Near-Infrared
Camera (NIRCam) and the Mid-Infrared Instrument (MIRI), the JWST has captured
one of the most detailed images of the nebula. In the two images JWST has
captured layers of gas and dust within the Southern Ring Nebula. Each layer has
been created by the expulsion of cosmic matter from the central dying star.
-
-
July 17, 2023 PLANETARY
NEBULAE - at center of Milkyway? 4097
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Friday, July 21, 2023
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