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An unprecedented discovery in space

Astronomers have discovered a two-faced and peculiar-looking star. One side of the star appeared to be mostly composed of hydrogen, while the other side seemed to be made of helium.

Published July 20,2023

Astronomers have discovered a star, which appears to have spontaneously developed two contrasting faces, for the first time. The object, located in the Cygnus constellation, at a distance of a thousand light-years, bears the scientific name ZTF J203349.8+322901.1. However, it has been named Janus after the two-faced Roman god.

At first, the discovery was made by the Zwicky Transient Facility (ZTF), which is an instrument scanning the night sky from the Palomar Observatory near San Diego.

Dr. Ilaria Caiazzo, an astrophysicist leading the research at Caltech, said, "The surface of the white dwarf changes completely from one side to the other. It's mind-boggling."

Caiazzo had been actively searching for white dwarfs, and one particular star stood out to her, due to the rapid changes in its brightness.

Further observations revealed that Janus rotates around its axis every 15 minutes.

Spectrometric measurements, which provide the chemical fingerprints of a star, showed that one side of the star consists almost entirely of hydrogen, while the other side is nearly pure helium.

Upon closer examination, both sides of the star appear bluish and possess similar luminosity. However, the helium side exhibits a streaked, patchy appearance similar to our Sun's, while the hydrogen side appears smooth.

White dwarfs are described as the cooling remnants of stars that were once like our Sun.

As stars age, they transform into red giants.

Eventually, the outer layers puff away, leaving behind a dense, hot, and fiery white dwarf with a mass roughly that of our Sun but condensed to the size of Earth.