What young stars tell us about the birth of our solar system
The familiar star at the center of our solar system has had billions of years to mature and ultimately provide us with life energy here on Earth. But a long time ago our sun was just a growing baby star. What did the sun look like when he was so young? It has long been a mystery that, if solved, could tell us about the formation of our solar system – so named because sol is the Latin word for sun – and other star systems made up of planets and stars. cosmic objects orbiting stars.
“We have detected thousands of planets in other star systems in our galaxy, but where do all these planets come from? Where does Earth come from? That’s what really motivates me,” says Catherine Espaillat, lead author of the article and an Associate Professor of Astronomy at Boston University College of Arts & Sciences.
A new research paper published in Nature by Espaillat and his collaborators finally provides new clues to the forces that were at play when our sun was in its infancy, detecting, for the first time, a single point of shape on a baby star which reveals new information on growth young stars.
When a small star forms, Espaillat explains, it eats dust and gas particles that swirl around it in what’s called a protoplanetary disk. The particles strike the star’s surface in a process called accretion.
“It’s the same process the sun went through,” says Espaillat.
Protoplanetary disks are found in magnetized molecular clouds, which throughout the universe are known to astronomers as fertile grounds for the formation of new stars. It has been theorized that protoplanetary disks and stars are connected by a magnetic field, and particles follow the field to the star. When the particles collide with the surface of the growing star, hot spots, extremely hot and dense, form at the focal points of the accretion process.
Looking at a young star about 450 million light-years from Earth, Espaillat and his team’s observations confirm, for the first time, the accuracy of accretion models developed by astronomers to predict the formation of hot spots. . These computer models have so far relied on algorithms that calculate how the structure of magnetic fields directs particles from protoplanetary disks to specific points on the surface of growing stars. Now observable data supports these calculations.
The BU team, comprising graduate student John Wendeborn and postdoctoral researcher Thanawuth Thanatibodee, closely studied a young star called GM Aur, located in the Taurus-Auriga molecular cloud of the Milky Way. It is currently impossible to photograph the surface of such a distant star, says Espaillat, but other types of images are possible since different parts of a star’s surface emit light in different wavelengths. . The team spent a month taking daily snapshots of the wavelengths of light emitted from the surface of GM Aur, compiling X-ray, ultraviolet (UV), infrared and visual data sets. To take a look at GM Aur, they relied on the “eyes” of NASA’s Hubble Space Telescope, the Transiting Exoplanet Survey (TESS) satellite, the Swift Observatory, and the Global Telescope Network. Las Cumbres observatory.
This particular star, GM Aur, completes a full rotation in about a week, and during that time the brightness levels are expected to peak and decrease as the brightest hot spot moves away from Earth and then turns around. to face our planet again. But when the team first aligned their data side-by-side, they were taken aback by what they saw.
“We saw that there was a lag [in the data] per day, ”explains Espaillat. Instead of all light wavelengths peaking at the same time, UV light was at its peak about a day before all other wavelengths peaked. At first, they thought they had collected inaccurate data.
“We went through the data so many times, rechecked the timing and realized it wasn’t a mistake,” she says. They found that the hot spot itself is not completely uniform and contains an area that is even hotter than the rest.
“The hot spot is not a perfect circle… rather it is an arc with part of the arc that is hotter and denser than the rest,” explains Espaillat. The unique shape explains the misalignment of the light wavelength data. This is a phenomenon in a hot spot never detected before.
“This [study] teaches us that hot spots are imprints on the stellar surface created by the magnetic field, ”explains Espaillat. At one time, the sun also had hot spots, different from sunspots, which are areas of our sun cooler than the rest of its surface – concentrated in areas where it ate particles from a surrounding protoplanetary disk of gas. and dust.
Eventually, the protoplanetary disks disappear, leaving behind stars, planets and other cosmic objects that make up a star system, Espaillat says. There is still evidence of the protoplanetary disk that powered our solar system, she says, found in the existence of our asteroid belt and all of the planets. Espaillat says studying young stars that share similar properties with our sun is key to understanding the birth of our own planet.
Watch out for the gap: Scientists use stellar mass to connect exoplanets to discs forming planets
CC Espaillat et al, Measurement of the density structure of an accretion hot spot, Nature (2021). DOI: 10.1038 / s41586-021-03751-5
Provided by Boston University
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