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In space, cataclysmic events happen to stars all the time. Some explode as supernovae, some get torn apart by black holes, and some suffer other fates. But when it comes to planets, stars turn the tables. Then it’s the stars who get to inflict destruction.

Expanding red giant stars consume and destroy planets that get too close, and a new study takes a deeper look at the process of stellar engulfment.

Stars like our Sun will eventually become red giants. Through nuclear fusion, they convert mass into energy (E=mc2, right?) Over their lifetimes, they shed so much mass as energy that they eventually expand and turn red. For planets that are too close to these swollen spheres, it spells the end. They’re eventually engulfed and completely destroyed.

A lot of research has delved into the planetary engulfment process, and a new study calculated one in ten evolved stars in the Milky Way will swallow Jupiter-mass planets.

The study is “Giant planet engulfment by evolved giant stars: light curves, asteroseismology, and survivability.” The first author is Christopher O’Connor. O’Connor is a Ph.D. student at the Department of Astronomy at Cornell University. The study has not been peer-reviewed yet.

The study focuses on two types of evolved stars that are closely related: Red Giant Branch (RGB) stars and Asymptotic Giant Branch (AGB) stars. The two are very similar, and in fact, RGB stars can become AGB stars. The term evolved star is descriptive enough to cover both, and in this work, the important thing is that RGB stars and AGB stars have both left the main sequence.

As these evolved stars lose mass, they expand, and at this stage, any planets in close proximity are in peril. The star’s convective envelope swells and ensnares the planet. This creates drag, which causes the planet to spiral inward toward the star. Astronomers know this, and in this work, the authors examined the frequency of these events and how the stars respond.

They describe a Sun-like star as a star with 1 to 2 solar masses. About 10% of these stars will engulf a planet between 1 to 10 Jupiter masses. For these mass relationships, the in-spiral will take between 10 and 100 years or between 100 and 1000 orbits.

To determine these ranges and how the star responds, the researchers used an open-source astronomy software tool called MESA (Modules for Experiments in Stellar Astrophysics.) “We use the Modules for Experiments in Stellar Astrophysics (MESA) software instrument to track the stellar response to the energy deposition while simultaneously evolving the planetary orbit,” they explain. MESA revealed how the different evolved stars responded to engulfing planets with different masses.

While many astrophysical events play out over thousands, millions, or even hundreds of millions of years, planetary engulfment is a much quicker process. But before the planet and star come into contact, two things draw them together: stellar expansion and orbital decay. This is the first phase of the engulfment, where tidal friction causes the planet’s orbital decay. The authors explain that the tidal friction is “most likely due to turbulent dissipation in the star’s convective envelope.” At this point in the process, drag from the stellar corona and the stellar wind are minimal.

Once the star and planet start to come into contact with one another, things change. Tidal friction takes a back seat to drag forces. The authors call this the ‘grazing’ phase. “The ‘grazing’ hydrodynamical interaction of the star and planet is complex and three-dimensional,” they write. The complexities in the grazing phase can include phenomena like the expulsion of matter from the star and optical and X-ray transients triggered by shocks. But this study leaves those phenomena aside for now. “We focus on the
later ‘inspiral’ phase of engulfment, when the planet is completely immersed in the envelope,” they write.

When a planet is in the inspiral phase, it deposits heat into the star. The latter part of this phase is called the late inspiral phase, and the heat added to the star during this phase is largely responsible for the star’s response. The mass of the planet is a determining factor in how much heat is deposited.

This figure from the paper shows heat deposited in stars in the later inspiral phase. The RGBs and AGBs are modelled host stars with different masses. The x-axis shows planetary mass, and the y-axis shows the amount of heat deposited. Clearly, the more massive the planet, the more heat is deposited. Image Credit: O'Connor et al. 2023. Did you miss our previous article…
https://mansbrand.com/meteorites-store-a-magnetic-memory-of-the-early-solar-system/

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Transporter-8 Mission

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June 10, 2023

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SpaceX is targeting Monday, June 12 for Falcon 9’s launch of the Transporter-8 mission to low-Earth orbit from Space Launch Complex 4E (SLC-4E) at Vandenberg Space Force Base in California. The 57-minute launch window opens at 2:19 p.m. PT (21:19 UTC). If needed, there is a backup opportunity Tuesday, June 13 with the same window.

The first stage booster supporting this mission previously launched NROL-87, NROL-85, SARah-1, SWOT, and four Starlink missions. Following stage separation, Falcon 9 will land on Landing Zone 4 (LZ-4) at Vandenberg Space Force Base.

Transporter-8 is SpaceX’s eighth dedicated smallsat rideshare mission. There will be 72 payloads on this flight, including CubeSats, MicroSats, a re-entry capsule, and orbital transfer vehicles carrying spacecraft to be deployed at a later time.

A live webcast of this mission will begin about 15 minutes prior to liftoff.

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Triggered Star Birth in the Nessie Nebula

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June 9, 2023

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Star formation is one of the oldest processes in the Universe. In the Milky Way and most other galaxies, it unfolds in cold, dark creches of gas and dust. Astronomers study sites of star formation to understand the process. Even though they know much about it, some aspects remain mysterious. That’s particularly true for the “Nessie Nebula” in the constellation Vulpecula. An international team led by astronomer James Jackson studies the nebula and its embedded star-birth regions. They found that it experienced a domino effect called “triggered star formation.”

“So, one of the interesting and open questions remaining in the field of star formation is, what happens when a star forms and ejects energy into the surrounding medium?” he said. “Does it make new stars, or does it prevent the formation of new stars?”

To answer those questions, Jackson and an international team of observers peered deep into the Nessie Nebula. It’s a so-called “Infrared Dark Cloud” (IRDC) with the official catalog name Lynds 772. Jackson named it the Loch Ness Monster Nebula a few years back. That’s because it resembles a spindly version of the famous and elusive Scottish lake monster. What the team found reveals that triggered star formation actually does take place under special circumstances in this nebula.

Putting the Nessie Nebula in Perspective

In 2013, Dr. Alyssa Goodman of Harvard Center for Astrophysics called the Nessie Nebula one of the “bones” of the Milky Way. That’s because it’s one of many webs of dusty filaments threaded through the galaxy. “It’s possible that the Nessie bone lies within a spiral arm, or that it is part of a web connecting bolder spiral features,” she said, noting that it probably spans at least 80 parsecs long and about a half-parsec wide.

As a galactic “bone”, it’s a prime place to look for triggered star formation. Nessie has a density of about 600 solar masses per parsec across its entire length. It’s also cold, with an average temperature of about 10K. There are many such cold clouds in the Milky Way, notably places like the famous Pillars of Creation or regions in the Carina Nebula.

The Pillars of Creation is another region of cold, dark gas similar to the Nessie Nebula where young stars are forming. Image Credit: NASA/ESA/CSA
The Pillars of Creation is similar to the Nessie Nebula where young stars are forming. Image Credit: NASA/ESA/CSA

A star gets started when gravity pushes the material in the cloud together to form a hot core. Temperatures and pressures rise, and eventually, a star is born. The Nessie Nebula is actually dense enough to form many very high-mass stars, according to Jackson. “By high mass, I mean a star that’s about 8 times the mass of the Sun, or more,” he said. “They have so much more energy than the Sun, and they inject this energy into the surrounding material, and they form these H II bubbles that ionize the gas around them.”

Essentially, those H II bubbles form as stellar winds from the hot young protostars push into surrounding space and photoionize (or heat) the gas there. As they expand, they stir up material around them. That creates a lot of energy. “The question I’m trying to answer is, does this energetic feedback trigger or hinder the formation of other new stars?” said Jackson.

The Domino Effect in the Nessie Nebula

The scenario for triggered star formation requires an almost perfect set of circumstances, starting with the cold dense nebula. Jackson explained that once a star (or group of stars) forms, its H II bubble triggers the birth process of the next star. That process repeats, almost like a domino effect.

So, does this triggered star formation really happen? Jackson pointed out two different scenarios. “If bubbles are just dispersing the gas, then that gas is gone and no stars can form,” he said. “On the other hand, if you have a clump of gas that’s almost ready to make a star, but not quite, can you hit it with an expanding shell and compress it? It could push it over the edge and gravity can take over. Some people say you make new stars and some say you don’t.”

To find out, the team looked at Nessie with the infrared-sensitive SOFIA flying observatory. It allowed them to peer through the clouds of gas and dust at the central region of the nebula. They coupled their observations with radio data from the Australia Telescope Compact Array and the Mopra radio dish. They zeroed in on its most luminous young stellar object, called AGAL337.916-00.477. This high-mass stellar object is part of a cloud in the nebula that has several other high-mass young stellar objects and so-called “dust cores” where the process of star

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New Detailed Images of the Sun from the World’s Most Powerful Ground-Based Solar Telescope

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June 9, 2023

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Our Sun continues to demonstrate its awesome power in a breathtaking collection of recent images taken by the U.S. National Science Foundation’s (NSF’s) Daniel Inouye Solar Telescope, aka Inouye Solar Telescope, which is the world’s largest and most powerful ground-based solar telescope. These images, taken by one of Inouye’s first-generation instruments, the Visible-Broadband Imager (VBI), show our Sun in incredible, up-close detail.

“These images preview the exciting science underway at the Inouye Solar Telescope,” Dr. Alexandra Tritschler, who is a National Solar Observatory Senior Scientist, tells Universe Today. “These images are a small fraction of the data obtained from the first Cycle. They exemplify the many and much broader science objectives and the much more powerful spectroscopy and spectropolarimetry data that now goes along with the images, none of which was available in 2020 when the Inouye Solar Telescope released its first-light images.”

The solar features in Inouye’s images include sunspots which reside in the Sun’s photosphere. These are the dark spots on the Sun’s “surface” and one of the Sun’s most well-known features, often reaching sizes that equal, or even dwarf, the size of the Earth. It is their dark appearance that can be deceiving, however, as sunspots are responsible for solar flares and coronal mass ejections that produce solar storms, which is a type of space weather.

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Image of a sunspot taken by the Inouye Solar Telescope. While they have a dark appearance, sunspots are responsible for solar flares and coronal mass ejections that produce solar storms. Sunspots often reach sizes that equal, or even dwarf, the size of the Earth. (Credit: National Science Foundation (NSF)/Association of Universities for Research in Astronomy, Inc. (AURA)/National Solar Observatory (NSO))
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Image of a sunspot with a light bridge, which is hypothesized to be the beginning stages of a degrading sunspot. (Credit: NSF/AURA/NSO)

Other features from the Inouye images include convection cells, which also reside in the Sun’s photosphere, and consist of upward- and downward-flowing plasma, known as granules or “bubbles”. The last feature in the Inouye images are fibrils, which exist in the Sun’s chromosphere and are produced from the magnetic field interactions within the Sun.

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Image of solar granules or “bubbles”, intergranular lanes, and magnetic elements in the quiet regions of the Sun. In these features, solar plasma rises in the
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