NEWS & PRESS
Astronomers have developed a way to detect the ultraviolet (UV) background of the Universe, which could help explain why there are so few small galaxies in the cosmos. UV radiation is invisible but shows up as visible red light when it interacts with gas. An international team of researchers led by Durham University, UK, has now found a way to measure it using instruments on Earth. The findings are published in a paper in Monthly Notices of the Royal Astronomical Society.
The researchers said their method can be used to measure the evolution of the UV background through cosmic time, mapping how and when it suppresses the formation of small galaxies. The study could also help produce more accurate computer simulations of the evolution of the Universe.
UV radiation – a type of radiation also given out by our Sun – is found throughout the Universe and strips smaller galaxies of the gas that forms stars, effectively stunting their growth. It is believed to be the reason why some larger galaxies like our Milky Way don’t have many smaller companion galaxies.
Simulations show that there should be more small galaxies in the Universe, but UV radiation essentially stopped them from developing by depriving them of the gas they need to form stars. Larger galaxies like the Milky Way were able to withstand this cosmic blast because of the thick gas clouds surrounding them.
Lead author Dr Michele Fumagalli, in the Institute for Computational Cosmology and Centre for Extragalactic Astronomy, at Durham University, said: “Massive stars and supermassive black holes produce huge amounts of ultraviolet radiation, and their combined radiation builds up this ultraviolet background.”
“This UV radiation excites the gas in the Universe, causing it to emit red light in a similar way that the gas inside a fluorescent bulb is excited to produce visible light.”
“Our research means we now have the ability to measure and map this UV radiation which will help us to further refine models of galaxy formation.”
Co-author Professor Simon Morris, in the Centre for Extragalactic Astronomy, Durham University, added: “Ultimately this could help us learn more about the evolution of the Universe and why there are so few small galaxies.”
Researchers pointed the Multi Unit Spectroscopic Explorer (MUSE), an instrument of the European Southern Observatory’s Very-Large Telescope, in Chile, at the galaxy UGC 7321, which lies at a distance of 30 million light years from Earth. MUSE provides a spectrum, or band of colours, for each pixel in the image allowing the researchers to map the red light produced by the UV radiation illuminating the gas in that galaxy.
The research, funded in the UK by the Science and Technology Facilities Council, could also help scientists predict the temperature of the cosmic gas with more accuracy.
Co-author Professor Tom Theuns, in Durham University’s Institute for Computational Cosmology, said: “Ultraviolet radiation heats the cosmic gas to temperatures higher than that of the surface of the Sun.”
“Such hot gas will not cool to make stars in small galaxies. This explains why there are so few small galaxies in the Universe, and also why our Milky Way has so few small satellite galaxies.”
Durham University Marketing & Communications Office
Dr Michele Fumagalli
Professor Tom Theuns
Images and animations
Details are as follows:
Movie showing the effect of ultraviolet (UV) radiation (indicated by the purple arrows) on the hydrogen gas surrounding the nearby spiral galaxy UGC 7321. As the gas is irradiated by the UV it begins to glow or fluoresce, allowing researchers to map the intensity of the UV radiation. The movie shows the field of view of the MUSE instrument at the European Very Large Telescope, which scientists used to detect the fluorescence.
Credit: M. Fumagalli/T. Theuns/S. Berry
Movie file Apostle movie.mp4:
This movie follows the formation of galaxies with cosmic time, illustrating how ultraviolet (UV) radiation from other galaxies and from quasars suppresses the formation of stars inside small galaxies near to large galaxies similar to the Milky Way and Andromeda.
The left panel shows a simulation that includes such diffuse UV radiation as in the real Universe, where fewer smaller galaxies form.
For comparison, the right panel shows what would happen in the absence of such radiation, with more small galaxies forming.
Credit: S. McAlpine/S. Berry
The new work appears in “A measurement of the z = 0 UV background from H-alpha fluorescence” Fumagalli, M, et al, Monthly Notices of the Royal Astronomical Society, Oxford University Press, DOI: 10.1093/mnras/stx398 (http://doi.org/10.1093/mnras/stx398)
Durham University’s academic experts are available for interview via down-the-line broadcast quality TV facilities from the Durham City campus, via broadcast provider Globelynx.
You can book the Globelynx fixed camera and circuit direct by logging into www.globelynx.com. The IFB number is +44 (0)191 384 2019.
If you have not booked a Globelynx feed before, or if you require any other support from Globelynx, please call +44 (0)20 7963 7174 (24 hours a day) for assistance.
A broadcast quality ISDN radio line is also available at Durham University and bookings can be arranged via the Marketing and Communications Office on the contact details above. The ISDN number is +44 (0)191 386 2749.
A landline number is available in our Media Suite which houses the television and radio facilities - +44 (0)191 334 6472.
Institute for Computational Cosmology: http://icc.dur.ac.uk/
Notes for editors
About Durham University
A world top 100 university with a global reputation and performance in research and education (QS and THE World University Rankings 2016/17; https://www.dur.ac.uk/about/rankings)
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 organizes 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 4,000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.
The RAS accepts papers for its journals based on the principle of peer review, in which fellow experts on the editorial boards accept the paper as worth considering. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content.