Skip to ContentSkip to Navigation
Part of University of Groningen
Science Linx News

'Polluted' white dwarfs show that stars and planets grow together

14 November 2022

Observations and simulations of 237 white dwarfs strengthen the evidence that planets and stars rapidly form together and become planetary systems. An international team of astronomers and planetary scientists, including Tim Lichtenberg of the University of Groningen's Kapteyn Institute, published their findings on Monday in Nature Astronomy.

Planets form in a disk of hydrogen, helium and small particles of ice and dust around a young star. The dust particles clump together and grow slowly at first. When enough of them are packed together, so-called planetesimals can form. These can subsequently grow into planets. Any debris is left behind as asteroids or planetesimals. That debris still occasionally slams into the star, providing a kind of fossil imprint of early geological processes.

Artistic impression of a planetesimal on collision course with a white dwarf star. | Illustration Amanda Smith / University of Cambridge
Artistic impression of a planetesimal on collision course with a white dwarf star. | Illustration Amanda Smith / University of Cambridge

White dwarfs

There is debate among astronomers and planetary scientists about whether stars form first and planets only many millions of years later, or whether planet formation begins almost simultaneously with the star. To answer this question, the researchers analyzed light from the atmosphere of 237 so-called polluted white dwarfs. These end-of-life stars are called polluted because, in addition to helium and hydrogen, they temporarily contain heavier elements in their atmosphere, such as silicon, magnesium, iron, oxygen, calcium, carbon, chromium and nickel.

‘The enrichment with heavy elements indicates that iron-core planetesimals have been falling onto the star,’ said Tim Lichtenberg, one of the study's authors. He was working at the University of Oxford when the research began and is now at the University of Groningen. “And such an iron core can likely only form if the fragment has been previously strongly heated. This is because that's when iron, rock and more volatile elements are separated.’

Tim Lichtenberg | Photo Kapteyn Institute / RUG
Tim Lichtenberg | Photo Kapteyn Institute / RUG


Additional simulations of asteroid collisions reinforce the observations and show that the debris falling into the stars must be quite small. "The iron cores, as with asteroids in our own solar system, were likely created by heat released during the decay of short-lived radioactive elements," Lichtenberg said. ‘We suppose that the element in question is aluminum-26. That element also drove the formation of planetary cores in our own solar system.’ Aluminum-26 has a half-life of about 700,000 years. As a consequence, the researchers argue that planet formation around what are now white dwarf stars must have occurred in the first few hundred thousand years of the stars’ lives.

In the future, the researchers plan to expand their research on white dwarf pollution. For example, the amounts of nickel and chromium in these "celestial graveyards" provide information about how large an asteroid or planetesimal was when its iron core formed. And that can give insights into atmospheric composition of Earth-like exoplanets.

Referentie: Amy Bonsor, Tim Lichtenberg, Joanna Drazkowska & Andrew M. Buchan: Rapid formation of exoplanetesimals revealed by white dwarfs , Nature Astronomy, 14 november 2022.

Text: NOVA

Last modified:15 November 2022 08.50 a.m.
View this page in: Nederlands

More news

  • 28 March 2023

    A leap of faith: from research to enterprise

    Having ideas, experimenting and trying things out, wanting to change society. For many researchers, all of this is day-to-day business. But what if you want to take your idea to market? This is a step that often does not come naturally to...

  • 14 February 2023

    Lift to the inclusive workplace

    There is plenty of work, and yet people with a disability are still often sidelined. One plus one is two, or so you’d think: this is the perfect time to help this group of workers find a job. The intention is there, also within the University, but...

  • 15 December 2022

    Groningen contributes to major research initiative into energy-efficient information technology

    The Dutch science funding agency NWO recently awarded a large research project into new concepts for energy-efficient information technology of no less than ten million euros