Astronomy: How do brown dwarfs form?

New observations provide insights into whether the birth of the giant planets takes a similar course to that of stars.

The birth of stars is a chaotic and dynamic process, especially in the early phase, which is characterized by complex gas structures in the form of spirals and streamers.

Such structures are termed "feeding filaments" because they feed the gaseous material from the surroundings to the newly born star, akin to cosmic umbilical cords.

Cosmic umbilical cord

Brown dwarfs are celestial objects with masses less than one-tenth of the mass of the Sun.

This makes them too small to undergo nuclear fusion and shine like stars.

Before now, scientists did not know whether brown dwarfs form like sun-like stars or not.

A test of this hypothesis requires high-sensitivity and high-angular resolution observations of brown dwarfs during their earliest formation stages.

An international team led by LMU astrophysicist Dr. Basmah Riaz from the University Observatory Munich has now accomplished just that: The researchers conducted observations of the extremely young brown dwarf, Ser-emb 16, using the highly sophisticated ALMA observatory in Chile and recently published their results in the journal Monthly Notices of the Royal Astronomical Society.

"Our observations have revealed spectacular large-scale spiral and streamer structures that have never been seen before towards a newly born brown dwarf," says Riaz.

The filaments cover a vast area of about 2,000-3,000 astronomical units and are connected to Ser-emb 16. Clumps of matter were also seen around it, which themselves could potentially evolve into young brown dwarfs.

"These observations show, for the first time, the influence of the external environment, which results in asymmetric mass accretion via feeding filaments on to a brown dwarf in the making," says the astronomer.

Collapsing clumps or magnetic cores?

The spiral structures and streamers provide important clues about how brown dwarfs form.

Having simulated possible scenarios, the researchers compared them with data from the ALMA observatory.

The large structures could be explained, for example, by collisions of collapsing clumps within a star-forming region.

For this to occur, such collisions would have to happen at least once during the lifetime of star-forming cores.

"We have shown through new numerical simulations that collisions trigger the collapse of even small clumps to form brown dwarfs. Spirals and streamers of various sizes and morphologies form due to the collisions happening sideways, not head-on," says co-author Dr. Dimitris Stamatellos from the University of Central Lancashire in England.

If this model is correct, it implies a dynamic brown dwarf formation process, similar to Sun-like stars, where chaotic interactions in a star-forming environment are common from an early age.

In another scenario, the simulations showed that the observed structures correspond to the large (pseudo)-disk around a very young brown dwarf, where the (pseudo)-disk has been twisted by the rotation of the brown dwarf core in the presence of a strong magnetic field.

If this model is correct, it means the magnetic field plays an important role in the brown dwarf formation process.

Read more at Science Daily

NASA's Webb captures an ethereal view of NGC 346

Filaments of dust and gas festoon this star-forming region in a new infrared image from MIRI.

One of the greatest strengths of NASA's James Webb Space Telescope is its ability to give astronomers detailed views of areas where new stars are being born. The latest example, showcased here in a new image from Webb's Mid-Infrared Instrument (MIRI), is NGC 346 -- the brightest and largest star-forming region in the Small Magellanic Cloud.

The Small Magellanic Cloud (SMC) is a satellite galaxy of the Milky Way, visible to the unaided eye in the southern constellation Tucana. This small companion galaxy is more primeval than the Milky Way in that it possesses fewer heavy elements, which are forged in stars through nuclear fusion and supernova explosions, compared to our own galaxy.

Since cosmic dust is formed from heavy elements like silicon and oxygen, scientists expected the SMC to lack significant amounts of dust. However the new MIRI image, as well as a previous image of NGC 346 from Webb's Near-Infrared Camera released in January, show ample dust within this region.

In this representative-color image, blue tendrils trace emission from material that includes dusty silicates and sooty chemical molecules known as polycyclic aromatic hydrocarbons, or PAHs. More diffuse red emission shines from warm dust heated by the brightest and most massive stars in the heart of the region. An arc at the center left may be a reflection of light from the star near the arc's center. (Similar, fainter arcs appear associated with stars at lower left and upper right.) Lastly, bright patches and filaments mark areas with abundant numbers of protostars. The research team looked for the reddest stars, and found 1,001 pinpoint sources of light, most of them young stars still embedded in their dusty cocoons.

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A star is born: Nearby galaxies provide clues about star formation

It is a popular notion that aside from large celestial objects like planets, stars and asteroids, outer space is empty. In fact, galaxies are filled with something called the interstellar medium (ISM) -- that is, the gas and dust that permeate the space in between those large objects. Importantly, under the right conditions, it is from the ISM that new stars are formed.

Now researchers from the University of California San Diego, in collaboration with a worldwide project team, have released their findings in a special issue of The Astrophysical Journal Letters dedicated to their work using advanced telescope images through the JWST Cycle 1 Treasury Program.

"With JWST, you can make incredible maps of nearby galaxies at very high resolution that provide amazingly detailed images of the interstellar medium," stated Associate Professor of Physics Karin Sandstrom who is a co-principal investigator on the project.

Although JWST can look at very distant galaxies, the ones Sandstrom's group studied are relatively close at about 30 million light years away, including one known as the Phantom Galaxy. Also known as M74 or NGC 628, astronomers have known of the Phantom Galaxy's existence since at least the 18th century.

Sandstrom, along with postdoctoral scholar Jessica Sutter and former postdoctoral scholar Jeremy Chastenet (now at University of Ghent), focused on a specific component of the ISM called polycyclic aromatic hydrocarbons (PAHs). PAHs are small particles of dust -- the size of a molecule -- and it's their small size that makes them so valuable to researchers.

When PAHs absorb a photon from a star, they vibrate and produce emission features that can be detected in the mid-infrared electromagnetic spectrum -- something that typically doesn't happen with larger dust grains from the ISM. The vibrational features of PAHs allow researchers to observe many important characteristics including size, ionization and structure.

This is something Sandstrom has been interested in since graduate school. "The Spitzer Space Telescope looked at the mid-infrared and that's what I used in my Ph.D. thesis. Since Spitzer was retired, we haven't had much access to the mid-infrared spectrum, but JWST is incredible," she stated. "Spitzer had a mirror that was 0.8 meters; JWST's mirror is 6.5 meters. It's a huge telescope and it has amazing instruments. I've been waiting a very long time for this."

Even though PAHs are not by mass a big fraction of the overall ISM, they're important because they're easily ionized -- a process that can produce photoelectrons which heat the rest of the gas in the ISM. A better understanding of PAHs will lead to a better understanding of the physics of the ISM and how it operates. Astrophysicists are hopeful JWST can provide a view into how PAHs are formed, how they change and how they're destroyed.

Because PAHs are evenly distributed throughout the ISM, they allow researchers to see not just the PAHs themselves, but everything around them as well. Previous maps, such as ones taken by Spitzer, contained much less detail -- they essentially looked like galactic blobs. With the clarity JWST provides, astrophysicists can now see gas filaments and even "bubbles" blown by newly formed stars, whose intense radiation fields and resulting supernova evaporate the gas clouds around them.

To get observation time on JWST, the Cycle 1 Treasury Program team had to design observations that included details such as exposure length and filters. Once their submission was accepted, Space Telescope Science Institute, which is responsible for the science and mission operations for JWST, captures and processes the data. This program includes data from 19 galaxies in total.

The Cycle 1 Treasury Program is part of a bigger project called PHANGS (Physics at High Angular Resolution in Nearby GalaxieS). PHANGS studies star formation and the ISM using multi-wavelength images from the Atacama Large Millimeter Array (ALMA) and the Very Large Telescope, both in Chile. However, because the dense clouds in which star formation happens contain a lot of dust, it is difficult for optical light to penetrate to see what's happening inside. Using the mid-infrared spectrum allows researchers to use that same dust and its bright emission to get high-resolution, detailed images.

"One of the things I'm most excited about is now that we have this high-resolution tracer of the ISM, we can map all kinds of things, including the structure of the diffuse gas, which has to become denser and molecular for star formation to occur," said Sandstrom. "We can also map the gas surrounding newly formed stars where there is a lot of 'feedback' such as from supernova explosions. We really get to see the whole cycle of the ISM in a lot of detail. That is the core of how a galaxy is going to form stars."

Read more at Science Daily

ALMA discovers birth cry from a baby star in the Small Magellanic Cloud

Researchers at Osaka Metropolitan University have observed "baby stars" in the Small Magellanic Cloud, having an environment similar to the early universe. Toward one of the baby stars, they found molecular outflow, which has similar properties to those seen in the Milky Way galaxy, giving a new perspective on the birth of stars.

The heavy elements in interstellar matter significantly impact the mechanism of star formation. In the early universe, the abundance of heavy elements was lower than in the present universe because there was not enough time for nucleosynthesis to produce heavy elements in stars. It has not been well understood how star formation in such an environment differs from present-day star formation.

An international team led by Professor Toshikazu Onishi, Osaka Metropolitan University, and Project Assistant Professor Kazuki Tokuda, Kyushu University/NAOJ, used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe high-mass young stellar objects in the Small Magellanic Cloud.

The Small Magellanic Cloud is characterized by a low abundance of elements heavier than helium, similar to the galaxies 10 billion years ago. The target provides a detailed observational view thanks to the relatively close distance from Earth. In this study, researchers detected a bipolar gas stream flowing out of the "baby star" Y246 and determined that the molecular flow has a velocity of more than 54,000 km/h in both directions.

In the present universe, growing "baby stars" are thought to have their rotational motion suppressed by this molecular outflow during gravitational contraction, accelerating the star growth. The discovery of the same phenomenon in the Small Magellanic Cloud suggests that this process of star formation has been common throughout the past 10 billion years. The team also expects this discovery to bring new perspectives to studying stars and planet formation.

From Science Daily