A Second Generation of Planets can Form Around a Dying Star

The workings of the Universe.
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fred8615
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A Second Generation of Planets can Form Around a Dying Star

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When young stars coalesce out of a cloud of molecular hydrogen, a disk of leftover material called a protoplanetary disk surrounds them. This disk is where planets form, and astronomers are getting better at peering into those veiled environments and watching embryonic worlds take shape. But young stars aren’t the only stars with disks of raw material rotating around them.

Some old, dying stars also have disks. Can a second generation of planets form under those conditions?

Planets form after stars form, but not long after. In our Solar System, the Sun formed about 4.6 billion years ago and the Earth about 4.5 billion years ago. Earth’s fate is entwined with the Sun’s fate. When the Sun expands as a red giant, it will expel layers of material into space and eventually expand enough to destroy the Earth and the other inner planets. Jupiter and the outer planets will survive, but they’ll likely spend the rest of their existence orbiting a white dwarf, the Sun’s remnant. No new planets can form around the white dwarf in this scenario.

But our Sun is a relative rarity. Many stars exist in binary pairs. Binary stars are the same age, but they have different masses. Since a star’s initial mass determines its future, the stars in a binary pair have different lifespans. If one of those stars has a similar mass as our Sun, it becomes a red giant and expels material out into space as it dies. What happens to all that material if the star has a binary partner?

This is where a new study comes into the picture. Its title is “A population of transition disks around evolved stars: Fingerprints of planets.” The first author is KU Leuven astronomer Jacques Kluska. The journal Astronomy and Astrophysics published the paper.

The gravitational pull of the second star can cause the ejected material from the dying star to form a new rotating disk very similar to the protoplanetary disk around the star when it was young. Astronomers already knew this could happen. What’s new is the evidence that a second generation of planets can form in the disk. According to this new study, new worlds are forming around 10% of binary stars in this situation.

“In ten percent of the evolved binary stars with discs we studied, we see a large cavity in the disc,” said first author Kluska in a press release. “This is an indication that something is floating around there that has collected all matter in the area of the cavity.”

Read more: https://www.universetoday.com/154386/a- ... ying-star/
Frederick J. Barnett
"Someone's got to take the responsibility if the job's going to get done!! Do you think that's easy?!" Gregory Peck - The Guns Of Navarone
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