- 4326 - BIGGEST STAR, BIGGEST PLANET? - Though the debate over what "counts" as a planet may seem arbitrary, it highlights big questions about what different planetary systems might look like, particularly those vastly different from ours. Our own solar system is just one of many innumerable outcomes?
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4326 - BIGGEST STAR,
BIGGEST PLANET?
-
- The biggest star
in the universe makes our sun look tiny speck
It is “UY Scuti”, a variable hypergiant with a radius around 1,700 times
larger than the radius of the sun.
-
- To put that in
perspective, the volume of almost 5 billion suns could fit inside a sphere the
size of UY Scuti.
-
- Our sun is
enormous, more than a million Earths could fit inside of it. But on a stellar
scale, it could be swallowed up by about half of all stars observed.
-
- In 1860, German
astronomers at the Bonn Observatory first cataloged UY Scuti, at the time
naming it “BD -12 5055”. During a second observation, astronomers realized it
grows brighter and dimmer over a 740-day period, leading to its classification
as a variable star.
-
- The star lies near
the center of the Milky Way, roughly 9,500 light-years away from Earth. Located
within the constellation Scutum, UY Scuti is a hypergiant star. Hypergiants
that are larger than supergiants and giants,
are rare stars that shine very brightly. They lose much of their mass
through fast-moving stellar winds.
-
- However, all
stellar sizes are estimates. The
complication with stars is that they have diffuse edges. Most stars don't have a rigid surface where
the gas ends and vacuum begins, which would have served as a harsh dividing
line and easy marker of the end of the star.
-
- Instead,
astronomers rely on a star's photosphere to determine its size. The photosphere
is where the star becomes transparent to light and the particles of light, or
photons, can escape the star. This is
the surface of the star, as this is the point at which photons can leave the
star.
-
- If UY Scuti
replaced the sun in the center of the solar system, its photosphere would
extend just beyond the orbit of Jupiter. The nebula of gas ejected from the
star extends far beyond the orbit of Pluto, to 400 times the distance between
the Earth and the sun.
-
- UY Scuti's large
radius does not make it the most massive, or heaviest, star. That honor goes to
“R136a1”, which weighs in at about 300 times the mass of the sun but only about
30 solar radii. UY Scuti, in comparison, is only about 30 times the mass of the
sun, but far greater in volume.
-
- Size comparisons
are still more complicated because UY Scuti doesn't remain stagnant. The star varies in brightness as it varies
in radius. And the measurement we have now has a margin of error of about 192
solar radii.
-
- The variation or
margin of error each could allow other stars to beat out UY Scuti in the race
for size. In fact, there are as many as 30 stars whose radii approach or
surpass UY Scuti's smallest estimated size.
-
- Which star would
take UY Scuti's place if its size were reevaluated? Here are a few that could
take the crown from the giant currently measured at 1,700 times the width of
the sun:
-
- WOH G64 was once
thought to measure a whopping 3,000 times the width of the sun. Newer
measurements put it at around 1,504 suns wide.
It is a red hypergiant star in the Large Magellanic Cloud, which is a
satellite galaxy of the Milky Way. Like UY
-
- Scuti, WOH G64
varies in brightness.
-
- Westerlund 1-26,
which measures more than 1,500 times the width of the sun, according to NASA.
-
- NML Cygni is
measured at 1,639 times the width of the sun, according to a 2012 paper in the
journal Astronomy and Astrophysics.
-
- KY Cygni measures
close to 1,033 times the width of the sun, according to a 2020 paper in the
journal Astrophysics of Galaxies.
-
- VY Canis Majoris
has been most recently measured to be about 1,420 times the width of the sun.
This red hypergiant star was once estimated to be 1,800 to 2,200 times the
width of the sun, but new measurements brought it down to size.
-
- What is the biggest
planet ever found? The universe is vast
and in the scheme of things, our planet is tiny. Even in our own solar system,
Earth is dwarfed by gas giants like Jupiter.
-
- The answer depends
on several factors, including how you define a planet. Even so, there are a few
candidates for the largest known planet. One of the largest is called “ROXs
42Bb”, a gas giant orbiting a star about 460 light-years from Earth. It is about
nine times the mass of Jupiter and has a radius of about 2.5 that of Jupiter.
-
- ROXs 42Bb from
data from the Keck Space Telescope.
-
- Two protoplanets
both orbit the star PDS 70 about 370 light-years from Earth and have a radius
between two and four times that of Jupiter.
-
- Another candidate
for the largest planet, HAT-P-67 b, had a radius larger than two times that of
Jupiter, which is similar to ROXs 42Bb.
-
- Objects are
detected using the transit method, which is when an object appears to cross in
front of its host star during its orbit and temporarily dims the star.
Exoplanets detected in this way, like HAT-P-67 b, can be directly measured.
-
- The other
uncertainty comes from the issue of how to define a planet. Though most people
know that stars are very large and planets are much smaller, there's a middle
ground, an object called a brown dwarf, which is too small to be a star but is
larger than a planet. Though the core of a brown dwarf is not hot enough to
fuse regular hydrogen like a star would, it can fuse deuterium, a special form
of hydrogen that contains a neutron.
-
- Scientists agree
that brown dwarfs are not planets. What's less clear is how to distinguish
between the two. Anything above 13
Jupiter masses is a brown dwarf and anything below is a planet.
-
- Typically,
planets like Jupiter form a rocky core, which attracts a disk of dust and gas
that gradually becomes a globular planet. ROXs 42Bb may have formed in a
different way, where parts of the dust and gas disk were so massive and heavy
that they collapsed in on themselves.
-
-
January 23, 2023
BIGGEST STAR, BIGGEST
PLANET?
4326
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Wednesday, January 24, 2024 ---------------------------------
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