Identification of young stars and their protoplanetary disks

Imagine you are walking through a thick fog in the middle of the night, seeing spots of light from cars and cities shimmering in the distance. It is almost impossible to determine whether the lanterns are deep in the fog or outside. Astronomers trying to find young stars face a similar problem: light from the stars they hunt shimmers through large areas of nebulous gas and dust in space called molecular clouds.

But the hearts of these clouds are often a hotbed young stars and planets, ideal places to try to figure out how celestial bodies are formed – provided astronomers can see what’s going on in the dark.

Now a team of scientists from the Department of Astronomy BU has come up with an inexpensive way to cut through the fog. They developed a new method that measures the dust cloud nebula and detects the presence of planetary structures known as protoplanetary disks – disks of gas and dust that are present around young stars and provide material for the planets. to form. They used their technique to get a better idea of ​​the interior of a molecular dust cloud located 450 light-years from Earth, in the constellation Taurus. There the two-star system is still in its infancy, its protoplanetary disks are still present and are probably in the process of creating several new planets.

“We’re actually trying to look through the fog of the cloud to see what these stars are doing, they’re like flashlights shining through the clouds,” said Dan Clemens, a professor at the College of Arts and Sciences and the Department of Astronomy and lead author of the article. used for a closer look at the planetary disks of the stars. The findings were published in Astrophysical Journal.

Scientists do not know exactly how stars and planets are formed, although they know some ingredients, including gas, dust, gravity and magnetic fields, so studying such systems can give an idea of ​​how the process unfolds. In the Taurus cloud, a young star with low mass and a brown dwarf rotate around each other every half a million years – the brown dwarf is sometimes called a failed star because it does not combine hydrogen and helium like bright stars. Both the brown dwarf and the young star have protoplanetary disks that surround them.

The BU team first studied disks in the Taurus cloud when Anelise Rillinger, a fifth-year graduate student at the BU Faculty of Astronomy, began studying the stellar system using radio waves assembled by the Large Millimeter Atacama Massif (ALMA), the largest radio telescope in the world. Rillinger had a previously published study with Catherine Espilat, associate professor of CAS astronomy and co-author of a new paper examining disks surrounding stars, and detailed modeling of disk structures.

Her work using radio waves aroused the interest of Clemens, who then, along with other members of his team, including Rillinger, Espaylat, and senior BU researcher Tushar Pilai, set out to test Rillinger’s observations of the same system, using almostinfrared light-the wavelength is less than radio waves, a little more than what the human eye can detect on its own. They wanted to show that it is possible to accurately model the location of disks using alternative – and, as a result, more accessible – tools.

When stars emit light, it is unpolarized (meaning that light waves travel in several directions). But when light passes through a dense molecular cloud, that light is polarized – light waves oscillate in one direction – due to the properties of dust and magnetic field built into the cloud. The researchers used an near-infrared polarimeter at the Perkins Telescope Observatory to measure the polarization of light passing through the cloud. The polarization measurement allowed the research team to see the signatures of the stars, which could tell them the orientation of the disks. The task was to subtract the effects of the surrounding cloud to find out the exact nature of the light coming from the stars, and to find out the orientation of the protoplanetary disks – the search for dust in the dust cloud.

The team confirmed that the near-infrared polarization data matched the radio wave data, showing that protoplanetary disks could be measured without large-scale instruments such as ALMA. Their work has also revealed something interesting in the system: the disks are in a strange alignment that astronomers often do not see – parallel to each other and located perpendicular to the magnetic field of a larger cloud. often protoplanetary disks rotates parallel to the magnetic field of the dust cloud, making this system rare and giving researchers the opportunity to gain a new insight into how disks form planets.

“It was an exciting and challenging task to develop knowledge about how to remove the cloud contribution from the internal polarizations of stars and young stellar objects – something we haven’t done before,” says Clemens. “The polarimetry in the near-infrared infrared range we conducted offered our own unique information about the disks, as well as the ability to look deeply into these optically opaque areas where new stars are forming.” Their tools can be used to check for the presence and orientation of disks in other deeply hidden areas of space.

Although they are still in the process of forming planets, the brown dwarf and young star in the Taurus cloud already seem to have smaller-mass mates who are on the border between the planets or perhaps another brown dwarf. In their piece of space the planets are likely to be formed over the next five million years.