Students map Milky Way with dwarf stars
|The Milky Way in the 2MASS infrared survey, similar to Hubble observations of the|
sky colour (near-infrared). Here, the visible stars are mostly bright giant stars
[Credit: The Infrared Processing and Analysis Center (IPAC)]
To find out exactly what the Milky Way looks like, astronomers have previously made maps using counts of the stars in the night sky. Leiden Astronomy students Isabel van Vledder and Dieuwertje van der Vlugt used the same technique in their research. Rather than studying bright stars, the two students used Hubble Space Telescope data from 274 dwarf stars, which were serendipitously observed by the orbiting observatory while it was looking for the most distant galaxies in the early Universe. The particular type of star they looked at were red dwarfs of spectral class M.
Dwarf stars are undersized and often have too low a mass to burn hydrogen. As warm, rather than hot objects, they are best viewed with near-infrared cameras. Van Vledder comments: "Astronomers believe that there are very many of these stars. That makes them really quite suitable for mapping the Galaxy even though they are so hard to find."
The model that includes both disk and halo was the perfect match. From the positions of the 274 M dwarfs in their sample, van Vledder and van der Vlugt inferred the existence of 58 billion dwarf stars. They were also able to accurately estimate the number of dwarfs in the halo, calculating a fraction of 7 per cent, higher than astronomers have previously found for the whole Milky Way.
The results of the students are important for future research with the European Space Agency’s Euclid Space Telescope, due for launch in 2020. Like Hubble, Euclid will image the whole sky in near-infrared. Van Vledder adds: "With our research, astronomers can now better assess whether they are dealing with a distant galaxy or a star in our own Galaxy." The students expect Euclid observations to yield an even more accurate picture of the Milky Way.
Van der Vlugt and van Vledder did the research for their bachelor’s degree in Astronomy at Leiden University. They worked together with Leiden astronomers Benne Holwerda, Matthew Kenworthy and Rychard Bouwens.
Source: Royal Astronomical Society [March 16, 2016]