Accretion discs: from quasars to planets
Lead Research Organisation:
University of Leicester
Department Name: Physics and Astronomy
Abstract
Discs occur throughout the Universe, from massive spiral galaxies to Saturn's rings. We have all seen an ice-skater spin faster as she pulls her arms closer to her body. The reason this happens is because angular momentum is conserved, and that same process, writ large, causes discs to form throughout the Universe. Most astrophysical objects form via gravitational collapse, and as gravity pulls material inwards it rotates progressively faster and faster, resulting in discs. Around stars and black holes these discs act as a conduit for infalling gas, and are called 'accretion discs'. Accretion on to a black hole is the most efficient means of energy generation we know of (many times more efficient than nuclear fusion), and consequently accretion discs are responsible for some of the most spectacular phenomena in the Universe. Accretion discs regulate the growth of super-massive black holes. We now believe that most, if not all, galaxies have super-massive black holes at their centres. These cosmic giants are many millions of times heavier than the Sun, and they have an enormously strong gravitational pull, and their formation appears to be intimately linked to the formation of the galaxies in which they reside. The 'feeding' of gas, through accretion discs, into super-massive black holes in distant galaxies is thought to be the engine that powers quasars, the brightest objects in the Universe. Locally, we now know that a super-massive black hole also lives at the centre of our galaxy, the Milky Way. This black hole is approximately four million times more massive than the Sun, but it is not currently being fed (thankfully for us!). Instead, it is surrounded by a rotating disc of very young stars, whose motions modern telescopes map with exquisite precision. The existence of these young stars was initially a puzzle, because the tenuous gas clouds which usually host star birth would be shredded by gravity so close to the black hole. We now believe that these stars formed during an earlier feeding episode, when the black hole's accretion disc broke apart under its own gravity. By studying our local super-massive black hole we can learn a great deal about the how black holes feed and form stars, and this in turn will enhance our knowledge of how black holes and galaxies form and grow in the distant Universe. Planets form in accretion discs around young stars. In recent years it has become clear that planets around other stars are common, with over 200 'extra-solar' planets now known. Accretion discs around young stars were the birthplaces of these distant solar systems. Within the discs around these young suns, dust and rocks stick together and eventually grow into planets. However, the solid material that makes up the building blocks for planets represents only a tiny fraction of the disc material; the vast majority of the disc is gaseous. Observations tell us that these discs live only for a few million years (a mere blink of the eye, in astrophysical terms), so understanding how their gas is removed is crucial to understanding how planets form. The processes of planet formation and disc evolution are inextricably linked, and only by understanding both can we hope to gain a full understanding of how planets form, and of how we came to exist. I will conduct large computer simulations of accretion discs, to study how stars form near super-massive black holes and how planets form in discs around young stars. Similar physics applies to both of these problems, despite their widely differing scales, so techniques developed in one context can readily be applied in the other. My research will show us how black holes form stars, and how star formation in turn regulates the growth of black holes at the centres of galaxies. On smaller scales I will simulate the formation of planets around young stars like our Sun, learning how accretion discs form violent 'hot Jupiters' and distant Earths.
People |
ORCID iD |
Richard Alexander (Principal Investigator / Fellow) |
Publications
Alexander R
(2012)
Galactic Centre star formation: the case of the missing gas disc The missing gas disc at the Galactic Centre
in Monthly Notices of the Royal Astronomical Society
Alexander R
(2012)
Deserts and pile-ups in the distribution of exoplanets due to photoevaporative disc clearing
in Monthly Notices of the Royal Astronomical Society: Letters
Alexander R
(2011)
Disc instability in RS Ophiuchi: a path to Type Ia supernovae?
Alexander R
(2015)
Magnetospheres of hot Jupiters: hydrodynamic models and ultraviolet absorption
in Monthly Notices of the Royal Astronomical Society
Alexander R
(2014)
Planet formation in evolving protoplanetary discs
in Proceedings of the International Astronomical Union
Alexander R
(2015)
Magnetospheres of hot Jupiters: hydrodynamic models & ultraviolet absorption
Alexander R
(2012)
THE DISPERSAL OF PROTOPLANETARY DISKS AROUND BINARY STARS
in The Astrophysical Journal
Alexander R
(2014)
Protostars and Planets VI
Alexander R
(2013)
Planet formation in evolving protoplanetary discs
Alexander R
(2011)
Disc instability in RS Ophiuchi: a path to Type Ia supernovae RS Oph and Type Ia SNe
in Monthly Notices of the Royal Astronomical Society
Ardila D
(2013)
HOT GAS LINES IN T TAURI STARS
in The Astrophysical Journal Supplement Series
Casewell S
(2012)
WD0837+185: THE FORMATION AND EVOLUTION OF AN EXTREME MASS-RATIO WHITE-DWARF-BROWN-DWARF BINARY IN PRAESEPE
in The Astrophysical Journal
Clarke C
(2016)
A self-similar solution for thermal disc winds
in Monthly Notices of the Royal Astronomical Society
Dunhill A
(2014)
Misaligned accretion on to supermassive black hole binaries
in Monthly Notices of the Royal Astronomical Society
Dunhill A
(2013)
The curiously circular orbit of Kepler-16b
in Monthly Notices of the Royal Astronomical Society
Dunhill A
(2013)
A limit on eccentricity growth from global 3D simulations of disc-planet interactions
in Monthly Notices of the Royal Astronomical Society
France K
(2012)
A HUBBLE SPACE TELESCOPE SURVEY OF H 2 EMISSION IN THE CIRCUMSTELLAR ENVIRONMENTS OF YOUNG STARS*
in The Astrophysical Journal
G. Martin R
(2013)
FORMATION OF CIRCUMBINARY PLANETS IN A DEAD ZONE
in The Astrophysical Journal
Hands T
(2016)
There might be giants: unseen Jupiter-mass planets as sculptors of tightly packed planetary systems
in Monthly Notices of the Royal Astronomical Society
Hands T
(2014)
Understanding the assembly of Kepler's compact planetary systems
in Monthly Notices of the Royal Astronomical Society
Harsono D
(2011)
Global gravitational instabilities in discs with infall Global GIs in discs with infall
in Monthly Notices of the Royal Astronomical Society
Ingleby L
(2013)
ACCRETION RATES FOR T TAURI STARS USING NEARLY SIMULTANEOUS ULTRAVIOLET AND OPTICAL SPECTRA
in The Astrophysical Journal
Ingleby L
(2011)
NEAR-ULTRAVIOLET EXCESS IN SLOWLY ACCRETING T TAURI STARS: LIMITS IMPOSED BY CHROMOSPHERIC EMISSION
in The Astrophysical Journal
Jones M
(2012)
The relationship between accretion disc age and stellar age and its consequences for protostellar discs Accretion disc age and stellar age
in Monthly Notices of the Royal Astronomical Society
Martin R
(2013)
Formation of circumbinary planets in a dead zone
Nichols J
(2015)
HUBBLE SPACE TELESCOPE OBSERVATIONS OF THE NUV TRANSIT OF WASP-12b
in The Astrophysical Journal
Owen J
(2010)
Radiation-hydrodynamic models of X-ray and EUV photoevaporating protoplanetary discs
in Monthly Notices of the Royal Astronomical Society
Pascucci I
(2011)
The Photoevaporative Wind from the Disk of TW Hya
Pascucci I
(2011)
THE PHOTOEVAPORATIVE WIND FROM THE DISK OF TW Hya
in The Astrophysical Journal
Wolf S
(2012)
Circumstellar disks and planets Science cases for next-generation optical/infrared long-baseline interferometers
in The Astronomy and Astrophysics Review
Description | We have gained increased understanding of how planets form around young stars, and how super-massive black holes grow. |
Exploitation Route | My findings are already widely used by other researchers seeking to understand planet formation and super-massive black holes. |
Sectors | Other |
URL | http://www.astro.le.ac.uk/~rda5/index.html |
Description | My findings have been published in a number of peer-reviewed international journals, and have been presented (both by me and others) at both national and international conferences. |
First Year Of Impact | 2009 |
Sector | Other |
Impact Types | Societal |
Description | ERC Consolidator Grant |
Amount | € 1,945,721 (EUR) |
Funding ID | 681601 |
Organisation | European Research Council (ERC) |
Sector | Public |
Country | Belgium |
Start | 06/2016 |
End | 05/2021 |
Description | Philip Leverhulme Prize |
Amount | £70,000 (GBP) |
Organisation | The Leverhulme Trust |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 07/2014 |
End | 07/2017 |
Description | Cafe Sci Talk |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Type Of Presentation | Keynote/Invited Speaker |
Geographic Reach | Local |
Primary Audience | Public/other audiences |
Results and Impact | Public talk on "Hunting for Exoplanets" at Cafe Scientifique, Nottingham, February 2013. - |
Year(s) Of Engagement Activity | 2013 |
Description | Nottingham Public Lecture |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Type Of Presentation | Keynote/Invited Speaker |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | Public lecture at the University of Nottingham, entitled "Exoplanets: Hunting for Other Worlds". - |
Year(s) Of Engagement Activity | 2013 |
Description | Pile-ups PR |
Form Of Engagement Activity | A press release, press conference or response to a media enquiry/interview |
Part Of Official Scheme? | No |
Type Of Presentation | Paper Presentation |
Geographic Reach | International |
Primary Audience | Media (as a channel to the public) |
Results and Impact | http://www2.le.ac.uk/offices/press/press-releases/2012/march/some-orbits-more-popular-than-others-in-solar-systems The press release and our subsequent interviews received widespread coverage in the science media (New Scientist, space.com, Astronomy Now, etc.). |
Year(s) Of Engagement Activity | 2012 |
Description | RPS talk |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Type Of Presentation | Keynote/Invited Speaker |
Geographic Reach | Local |
Primary Audience | Public/other audiences |
Results and Impact | Public talk on planets & black holes, hosted by Rushcliffe Photographic Society (Nottinghamshire). - |
Year(s) Of Engagement Activity | 2011 |
Description | Sky at Night |
Form Of Engagement Activity | A broadcast e.g. TV/radio/film/podcast (other than news/press) |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Public/other audiences |
Results and Impact | Appearance on BBC TV's "The Sky at Night", September 2015. |
Year(s) Of Engagement Activity | 2015 |
URL | http://www.bbc.co.uk/programmes/b06cbmpr |