“There really is dark matter out there,” says Dennis Zaritsky of the University of Arizona talking of the first evidence for this elusive cosmological substance, “Now we just need to figure out what it is.”
It was side-on views of two merging galaxy clusters made with state-of-the-art optical and X-ray telescopes that allowed Zaritsky and his colleagues to make this startling discovery. Dark matter is matter that does not emit or reflect enough electromagnetic radiation to be observed directly. Astronomers have assumed since the 1930s that most of the Universe must be composed of dark matter because of the way galaxies move through space. Our present understanding of gravity implies that the Universe must contain five times as much dark matter as normal matter.
Read the full story in my Spotlight physical sciences column on Intute.