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Re-Making Planets after Star-Death

Last Updated on Wednesday, 05 July 2017 10:39
Published on Wednesday, 05 July 2017 23:01

Astronomers Dr Jane Greaves, of the University of Cardiff, and Dr Wayne Holland, of the UK Astronomy Technology Centre in Edinburgh, may have found an answer to the 25-year-old mystery of how planets form in the aftermath of a supernova explosion. The two researchers will present their work on Thursday 6 July at the National Astronomy Meeting at the University of Hull, and in a paper in Monthly Notices of the Royal Astronomical Society.

Geminga-Labels smallData at wavelength of 0.45 mm, combined from SCUBA and SCUBA-2, in a false-colour image. The Geminga pulsar (inside the black circle) is moving towards the upper left, and the orange dashed arc and cylinder show the ‘bow-wave’ and a ‘wake’. The region shown is 1.3 light-years across; the bow-wave probably stretches further behind Geminga, but SCUBA imaged only the 0.4 light-years in the centre. Credit: Jane Greaves / JCMT / EAO. Click for a larger image

 

The first planets outside the solar system were discovered 25 years ago – not around a normal star like our Sun, but instead orbiting a tiny, super-dense 'neutron star'. These remnants are left over after a supernova, the titanic explosion of a star many times more massive than our own.

 

Such 'planets in the dark' have turned out to be incredibly rare, and astronomers are puzzled over where they come from. The supernova explosion should destroy any pre-existing planets, and so the neutron star needs to capture more raw materials to form its new companions. These after-death planets can be detected because their gravitational pull alters the times of arrival of radio pulses from the neutron star, or 'pulsar', that otherwise pass us by extremely regularly.

 

Greaves and Holland believe they have found a way for this to happen. Greaves explains: "We started looking for the raw materials soon after the pulsar planets were announced. We had one target, the Geminga pulsar located 800 light years away in the constellation of Gemini. Astronomers thought they'd found a planet there in 1997, but later discounted it because of glitches in the timing. So it was much later when I went through our sparse data and tried to make an image."

 

The two scientists observed Geminga using the James Clerk Maxwell Telescope (JCMT), which operates at submillimetre wavelengths, sited on Hawaii. The light the astronomers detected has a wavelength of about half a millimetre, is invisible to the human eye, and struggles to get through the Earth's atmosphere.

 

Holland, part of the group that built the JCMT camera the team used – called 'SCUBA' – notes: "What we saw was very faint. To be sure, we went back to it in 2013 with the new camera our Edinburgh-based team had built, SCUBA-2, which we also put on JCMT. Combining the two sets of data helped to ensure we weren't just seeing some faint artefacts."

 Geminga-Sketch smallSketch of the nebula formed by a wind of electrons and positrons coming from the pulsar, and the interaction with interstellar gas. Geminga crossed the plane of the Galaxy (off to the bottom right) around 100,000 years ago. It is thought that the supernova explosion was not symmetric, causing the remnant to recoil at around 200 km per second from its birth location. Credit: Jane Greaves / University of Cardiff. Click for a larger image

Both images showed a signal towards the pulsar, plus an arc around it. Greaves adds: "This seems to be like a bow-wave – Geminga is moving incredibly fast through our Galaxy, much faster than the speed of sound in interstellar gas. We think material gets caught up in the bow-wave, and then some solid particles drift in towards the pulsar."

 

Her calculations suggest that this trapped interstellar 'grit' adds up to at least a few times the mass of the Earth. So the raw materials could be enough to make future planets.

 

 

Greaves cautions that more data is still needed to tackle this quarter of a century old puzzle: "Our image is quite fuzzy, so we've applied for time on the international Atacama Large Millimetre Array – ALMA – to get more detail. We're certainly hoping to see this space-grit orbiting nicely around the pulsar, rather than some distant blob of Galactic background!"

 

If ALMA data confirm their new model for Geminga, the team hope to explore some similar pulsar systems, and contribute to testing ideas of planet formation by seeing it happen in exotic environments. This will add weight to the idea that planet birth is commonplace in the universe.

 


Media contacts

 

NAM press office (Monday 3 – Thursday 6 July)

Tel: +44 (0)1482 467507 / (0)1482 467508

 

Robert Massey

Royal Astronomical Society

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Anita Heward

Royal Astronomical Society

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Morgan Hollis

Royal Astronomical Society

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Jake Gilmore

STFC

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Science contacts

 

Jane Greaves

University of Cardiff

Mob: +44 (0)7599 628268

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Wayne Holland

UK Astronomy Technology Centre / University of Edinburgh

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Images and captions

 

Data at wavelength of 0.45 mm, combined from SCUBA and SCUBA-2, in a false-colour image. The Geminga pulsar (inside the black circle) is moving towards the upper left, and the orange dashed arc and cylinder show the ‘bow-wave’ and a ‘wake’. The region shown is 1.3 light-years across; the bow-wave probably stretches further behind Geminga, but SCUBA imaged only the 0.4 light-years in the centre. Credit: Jane Greaves / JCMT / EAO

 

Sketch of the nebula formed by a wind of electrons and positrons coming from the pulsar, and the interaction with interstellar gas. Geminga crossed the plane of the Galaxy (off to the bottom right) around 100,000 years ago. It is thought that the supernova explosion was not symmetric, causing the remnant to recoil at around 200 km per second from its birth location. Credit: Jane Greaves / University of Cardiff

 


Further information

 

The new work appears in: "The Geminga pulsar wind nebula in the mid-infrared and submillimetre", J. S. Greaves and W. S. Holland, Monthly Notices of the Royal Astronomical Society Letters, in press. A preprint of the paper is available here.

 


Notes for editors

 

Running from 2 to 6 July, the RAS National Astronomy Meeting 2017 (NAM 2017, http://nam2017.org) takes place this year at the University of Hull. NAM 2017 will bring together around 500 space scientists and astronomers to discuss the latest research in their respective fields. The conference is principally sponsored by the Royal Astronomical Society and the Science and Technology Facilities Council.

T: http://twitter.com/rasnam2017 

 

The Royal Astronomical Society (RAS, www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

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The Science and Technology Facilities Council (STFC, www.stfc.ac.uk) is keeping the UK at the forefront of international science and has a broad science portfolio and works with the academic and industrial communities to share its expertise in materials science, space and ground-based astronomy technologies, laser science, microelectronics, wafer scale manufacturing, particle and nuclear physics, alternative energy production, radio communications and radar.

STFC's Astronomy and Space Science programme provides support for a wide range of facilities, research groups and individuals in order to investigate some of the highest priority questions in astrophysics, cosmology and solar system science. STFC's astronomy and space science programme is delivered through grant funding for research activities, and also through support of technical activities at STFC's UK Astronomy Technology Centre and RAL Space at the Rutherford Appleton Laboratory. STFC also supports UK astronomy through the international European Southern Observatory. 

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