Survey profiles 350,000 stars in search for Sun’s lost siblings

​EMBARGOED UNTIL 10AM WEDNESDAY 18 APRIL 2018 (AEST)

Wednesday, April 18, 2018 — Astronomers from The Australian National University (ANU), other Australian institutions and Europe have mapped the chemical profiles of 350,000 stars in the Milky Way that will help them find the lost siblings of our Sun that were separated after birth by our galaxy.

The findings are from the first major public data release of the Galactic Archaeology survey, called GALAH, which was launched in late 2013 as part of a quest to uncover the formation and evolution of our galaxy.

Professor Martin Asplund from ANU said GALAH, when complete, would help reveal the original star clusters of the Milky Way, including the Sun's birth cluster and solar siblings along with more than one million other stars.

“This survey allows us to trace the ancestry of stars, showing astronomers how the Universe went from having only hydrogen and helium – just after the Big Bang – to being filled with all the elements we have here on Earth that are necessary for life,” said Professor Asplund from the Research School of Astronomy and Astrophysics and the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) at ANU.

Every star in the Sun’s birth cluster will have the same chemical composition – this cluster was quickly pulled apart by our Milky Way Galaxy and scattered across the sky.

Professor Asplund led the analysis of the survey data with PhD students Mr Sven Buder from the Max Planck Institute for Astronomy in Germany and Ms Ly Duong from ANU.  

“Measuring each chemical element abundance to get the stellar DNA for so many stars is an enormous challenge, but that’s exactly what we have done so this is a fantastic scientific achievement,” Professor Asplund said.

The GALAH survey is the brainchild of Professor Joss Bland-Hawthorn from the University of Sydney and ASTRO 3D and Professor Ken Freeman from ANU, and was conceived more than a decade ago as a way to unravel the history of our Milky Way galaxy.

This data will enable such discoveries as the original star clusters of the Galaxy, including the Sun's birth cluster and solar siblings – there is no other dataset like this ever collected anywhere else in the world.

Mr Buder is the lead author of the scientific article describing the GALAH data release.

“We train our computer code The Cannon to recognise patterns in the spectra of a subset of stars that we have analysed very carefully, and then use The Cannon’s machine learning algorithms to determine the amount of each element for all of the 350,000 stars,” he said.

Ms Duong and Professor Asplund worked with Mr Buder and European colleagues to develop the computer code.

The Cannon is named for Annie Jump Cannon, a pioneering American astronomer who classified the spectra of around 350,000 stars by eye over several decades a century ago – our code analyses that many stars in far greater detail in less than a day,” Ms Duong said.

The GALAH survey used the HERMES spectrograph at the 3.9-metre Anglo-Australian Telescope at the ANU Siding Spring Observatory to observe the different coloured light from stars that allow scientists to measure their chemical element abundance.

 

FOR INTERVIEWS:

Professor Martin Asplund
Research School of Astronomy and Astrophysics
ANU College of Science
T: +61 2 6125 0223
M: +61 426 807 567
E: martin.asplund@anu.edu.au

For media assistance, contact Will Wright on +61 2 6100 3486, the ANU media hotline on +612 6125 7979 or at <media@anu.edu.au>.

 

MULTIMEDIA FOR MEDIA USE:

Videos:

- Rainbow fingerprints – https://www.youtube.com/watch?v=2bVGr1MV2-8  

- Sky over the AAT – https://www.youtube.com/watch?v=6mRMj52V4DM  

- 2df night at the AAT – https://www.youtube.com/watch?v=XKoWQtDd14c  

Credit: The Australian Astronomical Observatory (AAO).

Click on this link to download high definition videos related to the research: https://drive.google.com/drive/folders/1kjbKBXQTvxtaJdrkVNtn9smWsDvmvR2L 

Credit: AAO

 

 

SUPPLEMENTARY INFORMATION:

Co-lead researcher Dr Gayandhi De Silva, from the University of Sydney and Australian Astronomical Observatory, said no other survey had been able to measure as many elements for as many stars as GALAH.

“This data will enable such discoveries as the original star clusters of the Galaxy, including the Sun's birth cluster and solar siblings – there is no other dataset like this ever collected anywhere else in the world,” Dr De Silva said.

Dr Sarah Martell from UNSW Sydney, who leads GALAH survey observations, said that the Sun, like all stars, was born in a group or cluster of thousands of stars.

“Every star in that cluster will have the same chemical composition or DNA – these clusters are quickly pulled apart by our Milky Way Galaxy and are now scattered across the sky,” Dr Martell said.

“The GALAH team’s aim is to make DNA matches between stars to find their long-lost sisters and brothers.”

For each star, this DNA is the amount they contain of each of nearly two dozen chemical elements such as oxygen, aluminium, and iron.

Unfortunately, astronomers cannot collect the DNA of a star with a mouth swab but instead use the starlight, with a technique called spectroscopy.

The light from the star is collected by the telescope and then passed through an instrument called a spectrograph, which splits the light into detailed rainbows, or spectra.

Associate Professor Daniel Zucker, from Macquarie University and the Australian Astronomical Observatory (AAO), said astronomers measured the locations and sizes of dark lines in the spectra  to work out the amount of each element in a star.

“Each chemical element leaves a unique pattern of dark bands at specific wavelengths in these spectra, like fingerprints,” he said.

Dr Jeffrey Simpson of the AAO said it took about an hour to collect enough photons of light for each star, but the team can observe 360 stars at the same time using fibre optics.

The GALAH team have spent more than 280 nights at the telescope since 2014 to collect all the data.

Measuring the abundance of each chemical in so many stars is an enormous challenge. To do this, GALAH has developed sophisticated analysis techniques.

The GALAH survey’s data release is timed to coincide with the huge release of data on 25 April from the European Gaia satellite, which has mapped more than 1.6 billion stars in the Milky Way, making it by far the biggest and most accurate atlas of the night sky to date. 

In combination with velocities from GALAH, Gaia data will give not just the positions and distances of the stars, but also their motions within the Galaxy.

Professor Tomaz Zwitter from the University of Ljubljana in Slovenia said the results from the GALAH survey would be crucial to interpreting the results from Gaia.

"The accuracy of the velocities that we are achieving with GALAH is unprecedented for such a large survey," he said.

Dr Sanjib Sharma from the University of Sydney said the GALAH survey data would allow scientists, for the first time, to gain a detailed understanding of the history of our galaxy.

The GALAH survey receives support from the Australian Research Council. The ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) is a $40m Research Centre of Excellence funded by the Australian Research Council (ARC) and six collaborating Australian universities: The Australian National University, The University of Sydney, The University of Melbourne, Swinburne University of Technology, The University of Western Australia and Curtin University.

Science papers accompanying this media release has been submitted for publication in the international journals Monthly Notices of the Royal Astronomical Society and the Astronomy & Astrophysics:

  1. Buder et al. 2018a: The GALAH Survey: Second Data Release
  2. Quillen et al. 2018: The GALAH Survey: Stellar streams
  3. Duong et al. 2018: The GALAH Survey: properties of the Galactic disks
  4. Kos et al. 2018: The GALAH Survey: chemical tagging the Pleiades
  5. Buder et al. 2018b: The GALAH Survey: Chemo-dynamics of the Galaxy
  6. Simpson et al. 2018a: The GALAH Survey: co-orbiting stars and chemical tagging
  7. Simpson et al. 2018b: The GALAH Survey: GALAH and the Magellanic clouds
  8. Khanna et al. 2018: The GALAH Survey: Velocity fluctuations in the Milky Way
  9. Gao et al. 2018: The GALAH Survey: NLTE trends in the open cluster M67
  10. Zwitter et al. 2018: The GALAH Survey: Radial Velocity Library
  11. Kos et al. 2018: The GALAH Survey: Holistic spectroscopy