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Gravitational wave astronomy is still in its early stages. So far it has focused on the most energetic and distinct sources of gravitational waves, such as the cataclysmic mergers of black holes and neutron stars. But that will change as our gravitational telescopes improve, and it will allow astronomers to explore the universe in ways previously impossible.

Although gravitational waves have many similarities to light waves, one distinct difference is that most objects are transparent to gravitational waves. Light can be absorbed, scattered, and blocked by matter, but gravitational waves mostly just pass through matter. They can be lensed by the mass of an object, but not fully blocked. This means that gravitational waves could be used as a tool to peer inside astronomical bodies, similar to the way X-rays or MRIs allow us to see inside a human’s body.

This is the idea behind a recent study looking at how gravitational waves could be used to probe the Sun’s interior. The Sun is so incredibly hot and dense that light can’t penetrate it. Even light produced in the Sun’s core takes more than 100,000 years to reach the Sun’s surface. Our only information about the Sun’s interior comes from helioseismology, where astronomers study vibrations of the Sun’s surface caused by sound waves within the Sun.

In this new study, the team looks at how the gravitational waves of fast-rotating neutron stars could be used to study the Sun. Although a perfectly smooth rotating object doesn’t create gravitational waves, asymmetrical spinning objects do. Neutron stars can have deformations or mountainous rises caused by their interior heat or magnetic fields. If such a neutron star spins rapidly, it produces a continuous stream of gravitational waves. These gravitational waves are too faint to be observed by current telescopes, but the next generation of gravitational observatories should be able to detect them.

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he path of three neutron stars behind the Sun. Credit: Takahashi et al

Since neutron stars are quite common in the galaxy, some of them are positioned such that the Sun passes in front of them from our perspective. Of the more than 3,000 known pulsars, about 500 of them are good candidates for gravitational wave sources, and of those 3 of them are known to pass behind the Sun. The team used the profiles of these three pulsars as a starting point.

Since the Sun is transparent to gravitational waves, the only effect the Sun has on them is through its gravitational mass. As the waves pass through the Sun, they are gravitationally lensed a bit. The amount of lensing depends on the mass of the Sun and the distribution of that mass. The team found that with proper measurements, gravitational wave observations could measure the density profile of the sun with an accuracy of 3 sigma.

The three known pulsars are likely just a tiny fraction of the gravitational wave sources that pass behind the Sun. Most neutron stars have a spin orientation that doesn’t direct radio flashes in our direction, but they could still be used as gravitational probes. There are likely hundreds of fast-rotating neutron stars that pass behind the Sun over the course of a year. So as we are able to observe their gravitational waves, they should give us an excellent view inside our closest star.

Reference: Ryuichi Takahashi, Soichiro Morisaki, and Teruaki Suyama. “Probing the solar interior with lensed gravitational waves from known pulsars.” arXiv preprint arXiv:2304.08220 (2023).

The post Gravitational Waves From Pulsars Could Be Used to Probe the Interior of the Sun appeared first on Universe Today.

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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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Review: Mountain Hardwear Kor Airshell Hoody

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June 8, 2023

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Ultralight Wind Shell
Mountain Hardwear Kor Airshell Hoody

$150, 5.1 oz./145g (men’s medium)

Sizes: men’s S-XXL, women’s XS-XL

backcountry.com

After sweating hard on a sunny and humid June morning hiking up the headwall of Huntington Ravine—the steepest and hardest trail on Mount Washington—we hit the cool wind blowing across the mountain’s alpine terrain. I pulled on my Kor Airshell Hoody and it tamed that wind while breathing so well that the wet sun shirt against my skin dried out quickly. And that pattern of sweating and hitting wind kept repeating itself on that two-day, 21-mile hut trek in New Hampshire’s Presidential Range, providing plenty of opportunities for the Kor to show off its strengths.

This jacket also displayed excellent breathability when I wore it running hilly trails from the Boise Foothills to central Massachusetts, on spring days of cool wind and temps in the 50s and low 60s Fahrenheit—with me sweating hard on each occasion, but the jacket only getting slightly damp inside and drying in minutes when my exertion level dropped going downhill. I also tested this hoody mountain biking in breezy, partly sunny, 50-degree conditions; and during cool, windy periods while backpacking in the first week of April on a section of the Arizona Trail along the Gila River and in Arizona’s Aravaipa Canyon.

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Hi, I’m Michael Lanza, creator of The Big Outside. Click here to sign up for my FREE email newsletter. Join The Big Outside to get full access to all of my blog’s stories. Click here for my e-guides to classic backpacking trips. Click here to learn how I can help you plan your next trip.

The Mountain Hardwear Kor Airshell Hoody.
” data-image-caption=”Testing the Mountain Hardwear Kor Airshell Hoody in New Hampshire’s Presidential Range.
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