Jun 25, 2019 | Updated: 07:39 AM EDT

Smallest Star Size to Date Measured

Apr 17, 2019 09:17 AM EDT

(Photo : Center for Astrophysics | Harvard & Smithsonian)

Scientists in the VERITAS (Very Energetic Radiation Imaging Telescope Array System) Collaboration have published a paper in Nature Astronomy journal detailing the results of their work with the VERITAS array-located at the Center for Astrophysics' Fred Lawrence Whipple Observatory in Amado, Arizona-to measure the smallest apparent size of stars in the night sky known to date.

VERITAS is the world's most sensitive very-high-energy gamma-ray observatory that consists of a ground-based array of four, 12-m optical reflectors for gamma-ray astronomy located at the Center for Astrophysics | Harvard & Smithsonian, Fred Lawrence Whipple Observatory in Amado, Arizona.

Given the almost inconceivable vastness of the universe, being able to measure the most distant objects can often be quite difficult. Direct measurement even by the best of optical telescopes of any star on the night sky too distant from Earth is almost impossible, and scientists overcame these limitations using diffraction, which occurs when an object, like an asteroid, passes in front of a star, making a shadow called an occultation. "The incredibly faint shadows of asteroids pass over us every day," explained Dr. Tarek Hassan, DESY. "But the rim of the shadow isn't perfectly sharp. Instead, wrinkles of light surround the central shadow, like water ripples."

Their published results show that the first star (TYC 5517-227-1), located 2,674 light years away, is 11 times the diameter of the Earth's sun, a giant, and the second star was shown to be 2.17 times the diameter of our sun with an angular size of 0.094 milliarcseconds and this is the smallest angular size of a star ever measured directly, the team said.

The task according to them was not as easy as turning telescopes to the sky. "Asteroid occultations are difficult to predict," said Daniel. "The only chance to catch the diffraction pattern is to make very fast snapshots when the shadow of the occultation sweeps across the telescope."  In this case, this was achieved by taking 300 snapshots per second to detect the diffraction pattern in the shadow sweeping past the telescopes.  

"VERITAS telescopes are uniquely sensitive as we use them primarily for observing faint light from very-high-energy gamma rays and cosmic rays. While they do not produce images as elegant as those from traditional optical telescopes, they see and capture fast variations of light, and we estimate that they can analyze stars up to ten times farther away with extreme accuracy than optical telescopes using the lunar occultation method can."

VERITAS spokesperson associate professor John Quinn of the UCD School of Physics said: "This study opens up the opportunity to use VERITAS to study a whole variety of rapidly varying optical phenomena and it is fantastic to see this innovative use of the telescopes for scientific applications beyond which they were originally designed." 

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