- 4217 - EXOPLANETS - and merging galaxies? Exoplanets are planets outside our own solar system. We have 8 planets. Plus, several “dwarf planets' including Pluto. The Kepler spacecraft has discovered most of the confirmed exoplanets that we know of beyond our solar system. But its successor, TESS (Transiting Exoplanet Survey Satellite), is catching up. Over 5,000 exoplanets have been discovered.
--------------------- 4217 - EXOPLANETS - and merging galaxies?
- TESS’s
planet-hunting mission has a more refined goal than its predecessor, Kepler.
TESS was specifically built to detect exoplanets transiting in front of bright
stars in Earth’s neighborhood. It has found about 400 confirmed exoplanets, but
there’s a list of exoplanets awaiting confirmation that contains almost 6,000
candidates. You are not alone!
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- The “Validation of
Transiting Exoplanets” using Statistical Tools (VaTEST) project uses
statistical tools and machine learning to comb through all of TESS’s data,
looking for elusive exoplanets.
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- False positives
are a persistent problem in exoplanet science.
TESS is looking for tiny dips in starlight around distant stars caused
by an exoplanet passing in front of the star. One blip isn’t enough; we need
several, and there has to be a rhythm to them. But other things can give false
impressions of a transiting planet, for example, eclipsing binary stars. Even a
star’s natural variability can cloud the signals.
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- TESS has gathered
an enormous amount of data that has to be worked through, sorting out false
positives from real signals, and that’s what VaTEST does. It has validated 8 potential super-Earths
using a combination of ground-based telescope data, high-resolution imaging,
and the statistical validation tool known as “TRICERATOPS”
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- Planet Earth Masses Earth Radii
TOI-238b 3.6 1.6
TOI-771b 2.8 1.4
TOI-871b 3.8 1.6
TOI-1467b 4.4 1.8
TOI-1739b 4 1.7
TOI-2068b 4.4 1.8
TOI-4559b 2.7 1.4
TOI5799b 3.7 1.6
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- A keystone planet
is an idea that has its roots in biology. In biology, a keystone species is one
that defines an entire ecosystem. In exoplanet science, a keystone planet is a
planet that helps explain the overall population of exoplanets. It helps
explain the radius gap we see in exoplanet populations.
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- There’s a scarcity
of planets between 1.5 and 2 Earth radii. It’s probably caused by
photo-evaporation mass loss. A star’s powerful radiation, especially in X-ray
and UV emissions (XUV), can strip away a planet’s atmosphere over time,
possibly creating a dearth of 1.5 to 2 Earth radii planets.
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- It is noteworthy
that planets within the size range investigated herein are absent from our own
solar system, making their study crucial for gaining insights into the
evolutionary stages between Earth and Neptune.
These keystone planets play a pivotal role in advancing our
understanding of the radius-valley phenomenon around low-mass stars.
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- A histogram of
planets with given radii from a sample of 900 Kepler systems. The decreased
occurrence rate between 1.5 and 2.0 Earth radii is apparent. It's called the
radius gap, Neptune desert, and the Fulton gap. Six of the new planets sit in
this gap.
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- There’s another
concept that relates to super-Earths and the radius gap, and it focuses on why
some planets lose their atmospheres and fall below the gap and why others
don’t. It’s called the ‘cosmic shoreline,’ and it’s a statistical trend that
links exoplanets together.
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- The cosmic
shoreline is a dividing line between planets that have retained their
atmospheres and planets that have lost them due to XUV radiation from their
stars.
In this study, astronomers validate eight exoplanets using
TESS, ground-based transit photometry, high-resolution imaging, and a
statistical validation tool.
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- Not only are some
of these planets in the radius gap, but two of them are suitable for further
atmospheric study with the JWST and its powerful instruments. Two of these validated planets, TOI-771b and
TOI-4559b, are good for transmission spectroscopy using JWST.
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- The simulated the
atmospheres showing signs of carbon dioxide, water, and, most intriguingly,
methane. Methane can be a biosignature, though there’s a lot of uncertainty.
Finding it in any exoplanet atmosphere will help scientists understand its
presence more fully, whether it’s an actual biosignature or not.
-
-
- A century-old
mystery of how galaxies change shapes has been solved by considering 'survival
of the fittest' collisions between galaxies.
A 100-year-old mystery surrounding the "shape-shifting" nature
of some galaxies has been solved, revealing in the process that our Milky Way
galaxy did not always possess its familiar spiral appearance.
-
- New observations
show how the evolution of galaxies from one shape to another takes place, a
process known as “galactic speciation” . The research shows that clashes and
subsequent mergers between galaxies are a form of "natural selection"
that drives the process of cosmic evolution.
-
- This means that the
Milky Way's history of cosmic violence is not unique to our home galaxy. Nor is
it over. Astronomy now has a new
anatomy sequence and finally an evolutionary sequence in which galaxy
speciation is seen to occur through the inevitable marriage of galaxies
ordained by gravity.
-
- Galaxies come in
an array of shapes. Some, like the Milky Way, are composed of arms of
well-ordered stars revolving in a spiral shape around a central concentration
or "bulge" of stellar bodies. Other galaxies like Messier 87 (M87)
are composed of an ellipse of billions of stars chaotically buzzing around a disordered
central concentration.
-
- Since the 1920s,
astronomers have classified galaxies based on a sequence of varying galaxy
anatomy called the "Hubble sequence." Spiral galaxies like ours sit
at one end of this sequence, while elliptical galaxies like M87 sit at the
other. Bridging the gap between the two are elongated sphere-shaped galaxies,
lacking spiral arms, called lenticular galaxies.
-
- But what this
widely-used system has lacked until now were the evolutionary paths that link
one galaxy shape to another. This
revealed the existence of two different types of bridging lenticular galaxies:
One version that is old and lacks dust, and the other that is young and rich in
dust.
-
- When dust-poor
galaxies accrete gas, dust, and other matter, the disk that surrounds their
central region is disrupted, with said disruption creating a spiral pattern
radiating out from their hearts. This creates spiral arms, which are over-dense
rotating regions that create gas clumps as they turn, triggering collapse and
star formation.
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- The dust-rich
lenticular galaxies are created when spiral galaxies collide and merge. Spiral
galaxies have a small central spheroid with extending spiral arms of stars, gas
and dust. Young and dusty lenticular galaxies have notably more prominent
spheroids and black holes than spiral galaxies and dust-poor lenticular
galaxies.
-
- The surprising
upshot of this is the conclusion that spiral galaxies like the Milky Way
actually lie between dust-rich and dust-poor lenticular galaxies on the Hubble
sequence. The history of the Milky Way
is believed to be punctuated with a series of "cannibalistic" events
in which it devoured smaller surrounding satellite galaxies to grow.
-
- Our galaxy's
cosmic "acquisitions" also included it accreting other material and
gradually transforming from a dust-poor lenticular galaxy to the spiral galaxy
we know today. Our galaxy is set for a dramatic merger with its closest large
galactic neighbor, the Andromeda galaxy, in between 4 billion and 6 billion
years.
-
- Just as this new
galaxy will carry the story of its evolution for astronomers in the far-future,
the dust-poor lenticular galaxies could serve as fossil records of the
processes that transformed old and common disk-dominated galaxies in the early
universe.
-
- This could help
explain the discovery by the James Webb Space Telescope (JWST) of a massive
spheroid-dominated galaxy just 700 million years after the Big Bang. The new
research could indicate, too, that the merging of elliptical galaxies is a
process that could explain the existence of some of the universe's most massive
galaxies, which sit at the heart of clusters of over 1,000 galaxies.
-
-
November 11, 2023
EXOPLANETS - and merging galaxies? 4217
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