by Scientists have directly imaged eight faint stars that accompany very bright stars within the Gaia data catalogue, including so-called “failed stars”, known as brown dwarfs.
The stars and their companions were first identified from the millions of stars in the Gaia catalog. They were deemed suitable for follow-up investigations with the ground-based GRAVITY instrument, an advanced near-infrared interferometer located at the Very Large Telescope (VLT) at the summit of Cerro Paranal in Chile. By combining infrared light from multiple telescopes, a process known as interferometry, GRAVITY has already achieved the first direct observation of an extrasolar planet, or “exoplanet”.
Following up on the Gaia observations, GRAVITY directly observed light signals from companions around the eight bright stars, seven of which are theorized, so far undiscovered objects.
Three of the companion objects are small, faint stars, and the other five are brown dwarfs. The latter form are similar to stars and have more mass than gas giant planets, but do not have enough mass to fuel the fusion of hydrogen into helium in their cores as main sequence stars do. That’s where his nickname “failed stars” comes from.
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One of the brown dwarfs seen from gravity orbits its parent star at a distance equal to the distance between Earth and the sun. This is the first time one of the failed stars has been seen so close to its host star.
“We have shown that it is possible to capture an image of a faint companion, even when it orbits very close to its bright host,” team leader and European Southern Observatory (ESO) scientist Thomas Winterhalder said in a statement. “This achievement demonstrates the amazing synergy between Gaia and Gravity. Only Gaia can identify such tight systems where a star and companion are ‘hidden’, and then gravity can image the smaller and fainter object with precision unprecedented.”
Firefly on a lighthouse
Looking directly at faint objects such as small faint stars or brown dwarfs around bright stars is no trick. In fact, they seem to see their light signals and see the light of a firefly sitting on a shining lighthouse. Any attempt to imagine the light of the firefly is obviously washed out by the brighter light of the lighthouse, and the same is true of bright stars and their counterparts.
Although Gaia is unable to see the counterparts of these stars directly, the space telescope was able to infer their presence. This is because when a brown dwarf, or small star in general, orbits a larger and brighter star, its gravity pulls on the parent star and this creates a “swallow” in the motion of the larger and brighter star. brightness
As that star “slows” away from Earth (and Gaia), the wavelength of light lengthens, shifting it toward the red end of the electromagnetic spectrum. Conversely, when it moves towards Earth, the wavelengths of light are shortened, shifting the light towards the blue end of the electromagnetic spectrum.
This redshift and blueshift effect is analogous to the Doppler shift, the phenomenon that affects sound waves on Earth. For example, as an ambulance approaches you with its siren blaring, the sound waves are compressed, and the higher pitched horn is distorted, like a blueshift. As the ambulance passes you, the wavelengths of the sound stretch out, and the low hum is tilted, just like the shift of light from the star as it moves away.
This redshift and blueshift effect is small, but Gaia is sensitive enough to see it. The small companions of these stars in the Gaia sample lie at tiny angles separated from their bright parent stars by a few dozen milliarc seconds, which is about the size of a quarter when viewed from a distance of about 62 miles (100 kilometers) away.
“In our view, the Gaia data serves as a kind of signal,” explained Thomas. “The part of the sky we can see with gravity is very small, so we need to know where to look. Gaia’s unparalleled precision measurements of the movements and positions of the stars are essential to pointing our instrument in the right direction in the sky.”
The collaboration of Gaia and GRAVITY helped the team go beyond detecting these companions. The two data sets also enabled the team to separate the mass of the star and the mass of the companions. Furthermore, by measuring the differences in the wavelength of light from the stars and their companion bodies, as well as combining this information with the aforementioned mass estimates, the team was able to draw a conclusion. ages of the companions.
This indicated that the brown dwarfs were less luminous than expected at the observed ages and masses, suggesting that these bodies may have orbited another, smaller companion. and even smaller, perhaps even obscure exomoons.
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The power of the Gaia-GRAVITY tag team means that scientists could soon use these two instruments to image smaller companions around bright stars, namely exoplanets.
“The Gaia mission is unique in being able to tease out the tiny movements of nearby pairs in the sky. The next catalog, which will be made available as part of the fourth data release (DR4), will contain an even richer collection. stars with companions that may be smaller,” said Johannes Sahlmann, Gaia scientist of the European Space Agency (ESA). “This result breaks new ground in the search for planets in our galaxy and promises us insight into new life i far away.”
The team’s research was published on June 10 in the journal Astronomy and Astrophysics.
