Astronomers probe the structure of the brown dwarf’s atmosphere layer cake


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Jupiter may be the raw planet in our solar system because it is the most massive planet. But it is actually a runt compared to most of the giant planets found around other stars.

These alien worlds, called super-Jupiters, weigh up to 13 times the mass of Jupiter. Astronomers have analyzed the makeup of some of these monsters. But it has been difficult to study their atmospheres in detail as these gas giants get lost in the glow of their mother stars.

However, researchers have a substitute: the atmospheres of brown dwarfs, so-called failed stars that have up to 80 times the mass of Jupiter. These heavy objects form from a collapsing cloud of gas, like stars do, but lack the mass to get hot enough to sustain nuclear fusion in their core, which powers the stars.

Instead, brown dwarfs share a kinship with super-Jupiters. Both types of objects have similar temperatures and are extremely massive. They also have complex and varied atmospheres. The only difference, astronomers believe, is their pedigree. Super-Jupiters form around the stars; brown dwarfs often form in isolation.

A team of astronomers, led by Elena Manjavacas of the Space Telescope Science Institute in Baltimore, Maryland, tested a new way to peer into the cloud layers of these nomadic objects. The researchers used an instrument from the WM Keck Observatory in Hawaii to study the near infrared colors and variations in brightness of the layered cloud structure in the nearby floating brown dwarf known as 2MASS J22081363 + 2921215.

The Keck Observatory’s instrument, called the Multi-Object Spectrograph for Infrared Exploration (MOSFIRE), also analyzed the spectral fingerprints of various chemical elements contained in clouds and their evolution over time. This is the first time that astronomers have used the MOSFIRE instrument in this type of study.

These measurements gave Manjavacas a holistic view of the atmospheric clouds of the Brown Dwarf, providing more detail than previous observations of this object. Initiated by the observations of Hubble, this technique is difficult to implement for telescopes on the ground because of the contamination of the Earth’s atmosphere, which absorbs certain infrared wavelengths. This absorption rate changes depending on weather conditions.

“The only way to do it from the ground is to use the high resolution MOSFIRE instrument as it allows us to observe multiple stars simultaneously with our brown dwarf,” Manjavacas explained. “This allows us to correct for contamination introduced by the Earth’s atmosphere and to measure the true signal of the brown dwarf with good precision. Thus, these observations are a proof of concept that MOSFIRE can do this type of dwarf studies. brown atmospheres. “

Manjavacas will present its results on June 9 at a press conference during the virtual meeting of the American Astronomical Society.

The researcher decided to study this brown dwarf in particular because it is very young and therefore extremely bright and has not cooled down yet. Its mass and temperature are similar to those of the neighboring giant exoplanet Beta Pictoris b, discovered in 2008 in near infrared images taken by the very large telescope of the European Southern Observatory in northern Chile.

“We do not yet have the capacity with current technology to analyze in detail the atmosphere of Beta Pictoris b,” said Manjavacas. “So we’re using our study of this brown dwarf’s atmosphere as a proxy to get an idea of ​​what the exoplanet’s clouds might look like at different heights of its atmosphere.”

The brown dwarf and Beta Pictoris b are both young, so they emit heat in the near infrared strongly. They are both members of a group of stars and sub-stellar objects called the Beta Pictoris mobile group, which share the same origin and common movement in space. The cluster, which is around 33 million years old, is the closest cluster of young stars to Earth. It is located about 115 light years away.

Although they are cooler than bona fide stars, brown dwarfs are still extremely hot. The brown dwarf in the Manjavacas study is 2,780 degrees Fahrenheit (1,527 degrees Celsius).

The giant object is about 12 times heavier than Jupiter. As a young body, it spins incredibly fast, rotating every 3.5 hours, compared to Jupiter’s 10 hour spin period. Thus, the clouds whip him, creating a dynamic and turbulent atmosphere.

The Keck Observatory’s MOSFIRE instrument watched the brown dwarf for 2.5 hours, observing how light filtering through the atmosphere from the warm interior of the dwarf brightened and darkened over time. The bright spots that appear on the rotating object indicate regions where researchers can see deeper into the atmosphere, where it is warmer. Infrared wavelengths allow astronomers to peer deeper into the atmosphere. Observations suggest that the brown dwarf has a mottled atmosphere with scattered clouds. Seen up close, it might look like a carved Halloween pumpkin, with light escaping from its warm interior.

Its spectrum reveals clouds of hot sand grains and other exotic elements. Potassium iodide traces the object’s upper atmosphere, which also includes clouds of magnesium silicate. Descending into the atmosphere is a layer of clouds of sodium iodide and magnesium silicate. The final layer consists of clouds of aluminum oxide. The total depth of the atmosphere is 446 miles (718 kilometers). The detected elements represent a typical part of the makeup of brown dwarf atmospheres, Manjavacas said.

The researcher and her team used computer models of brown dwarf atmospheres to determine the location of chemical compounds in each cloud layer.

Manjavacas’ plan is to use the Keck Observatory’s MOSFIRE to study other atmospheres of brown dwarfs and compare them to those of gas giants. Future telescopes like NASA’s James Webb Space Telescope , an infrared observatory slated to launch later this year, will provide even more information about the atmosphere of a brown dwarf. “JWST will give us the structure of the entire atmosphere, providing more coverage than any other telescope,” Manjavacas said.

The researcher hopes that MOSFIRE can be used in tandem with JWST to sample a wide range of brown dwarfs. The goal is a better understanding of brown dwarfs and giant planets.

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