Researchers from the Konkoly Thege Miklós Astronomical Institute of the ELKH Research Centre for Astronomy and Earth Sciences (CSFK) have been involved in the engineering design process for the WEAVE (WHT Enhanced Area Velocity Explorer) instrument, which recorded its first scan of the sky in December 2022. One of the goals of the UK-led international sky scanner project WEAVE is to examine the development of stars and galaxies, and the structure of the Milky Way. The Hungarian researchers will also be involved in examining the chemical evolution of the Milky Way, pulsating variable stars, and quasars.
The William Herschel Telescope, which has been used in astronomical research for 35 years, is located at the top of a 2,400-meter-high volcano on La Palma Island in the Canary Islands. A state-of-the-art multi-object spectrograph has now begun operation after ten years of planning and development work on the 4.2-meter telescope. The uniqueness of the spectrograph lies in the fact that it uses independent optical fibers to produce spectra encompassing up to a thousand objects at a time. WEAVE will eventually complete eight separate sky scanning programs. Over the next five years, the instrument will help researchers record approximately 12 million spectra of different stars and galaxies. These will provide data on the chemical and physical state of stars, galaxies, and interstellar and intergalactic gas. In combination with the monitoring data of the European Space Agency's Gaia space telescope and the LOFAR (Low Frequency Array) radio telescope system, it will provide information about both our own galaxy and distant galaxies. By using quasars – the supermassive black holes at the cores of distant galaxies – as lighthouses, the spatial structure of the gas around galaxies and its interaction with galaxies can be studied in a state that is tens of billions of years earlier than the present universe.
The instrument uses optical fibers to examine the light of celestial bodies. The optical fibers split light by wavelength into two different spectrographs. The images prepared in this way are recorded on large-scale CCD cameras. The WEAVE instrument has three different modes. With the first (LIFU), 547 optical fibers are placed close to each other in a hexagonal formation to allow them to examine widely spread objects, such as the velocity distribution of individual sub-systems within galaxies. In the second mode (MOS), robots adjust the fibers (up to 960) in order to capture the spectra of individual stars, galaxies and quasars with a single exposure. In the third (mIFU) mode, 20 separate units can accommodate up to two sets of 37 optical fibers, enabling the examination of objects, such as nebulae and galaxies, that are less widely spread.
In the first recording from the sky (the “first light” image), two independent galaxies in the Pegasus constellation were captured. These are located 280 million light years away. The galaxies NGC 7318a and NGC 7318b are part of the famous Stephan's Quintet, a cluster of galaxies observed by the Hubble and Spitzer space telescopes, the Chandra X-ray telescope and, more recently, the James Webb Space Telescope, in addition to WEAVE. The spectra of the galaxies consisted of the light of many millions of stars. WEAVE recorded 547 spectra, from the ultraviolet to the near-infrared at unique points on and around the visible surfaces of the two galaxies. Among other things, these spectra help reveal the movement of stars and gas, the chemical composition of stars, and the temperature and density of gas clouds. This will also make it possible to study the evolution of galaxies and their interactions.
The three research fields of the Hungarian experts – examining the chemical evolution of the Milky Way, pulsating variable stars, and quasars – are connected to three Momentum programs at the CSFK Konkoly Thege Miklós Astronomical Institute. The first, which has already been completed, was led by Maria Lugaro, the second, led by Róbert Szabó, is in its final year, while the third, led by András Kovács, is a five-year project that began in December 2022. Quality control of the preliminary data is underway as part of the latter project, and cosmological simulations are also being prepared that can be compared against the data.
After the initial trial scans, WEAVE has now begun its routine operations, and we can soon look forward further scientific findings with Hungarian involvement.
Left: The William Herschel Telescope with the WEAVE instrument. The optical fiber positioning device is in the black box on top, the spectrograph itself is in the grey box on the left. Optical fibers run through the structure of the telescope (source: Sebastian Kramer).
Right: Image from the James Webb telescope of the Stephan's Quintet galaxy cluster recorded with WEAVE’s 547 optic fibers. Each tiny circle corresponds to 2.6 arcseconds in the sky. The hundreds of individual spectra also provide information about the physical processes taking place both in galaxies and in intergalactic space. Source: NASA, ESA, CSA, STScI (background); Aladin (optical fibers).