Captured in an image by UC Santa Cruz astronomers, an illuminated piece of the intergalactic cosmic web, lovingly named “Slug Nebula,” has been recognized by Physics World magazine as one of the “Top Ten Breakthroughs in Physics of 2014.”
Since the universe is constantly expanding and evolving, many astronomers and astrophysicists are faced with the question of what, if anything, is between galaxies. In the last 20 years, scientists have put together refined pictures via supercomputer simulations of a potential structure of our universe, the cosmic web.
The cosmic web is a network composed of threadlike filaments (similar to that of a spider’s web) of dark matter and gas that connect the Milky Way to all other galaxies throughout the universe. Computer simulations point to its existence, suggesting the organization of the universe is not random, but until now no real data or imagery determined what it is that connects our universe.
“Most of the material out there is very low-density, much less than the atmosphere,” said astronomy and astrophysics Professor J. Xavier Prochaska. “This material is so faint you can’t detect it with just a telescope. An approach is to detect the gas and absorption by shining light through it and seeing how it gets modulated.”
The light source used in this discovery was actually a nearby galaxy, or a quasar. A quasar is a special type of galaxy with black holes at its center. Quasars are surrounded by spinning discs of scorching material that illuminate surrounding gas millions of light-years away. The quasar acts as the flashlight needed to illuminate the cosmic web filament, which extends about 2 million light-years across our universe.
Despite the favorable circumstances, capturing this image required the most advanced and sought-after equipment in the world. The image was first captured at Keck Observatory on the summit of Mauna Kea in Hawaii — home to two of the largest optical and infrared telescopes in the world, each of which weighs about 300 tons, stands eight stories tall and operates with exact nanometer precision.
However, use of the observatory is expensive. The University of California spends $13 million per year for access to the Keck telescopes. The project also required UCSC researchers to construct a $10,000 custom light filter that was fitted to the lens of the Keck Observatory’s camera.
“I had no particular expectations,” said research team leader Sebastiano Cantalupo. “When we saw, already in the first image, the huge Nebula around the quasar in the image, my colleagues and I were completely shocked.”
Cantalupo and his team traveled to Hawaii to research dark galaxies — ones primarily composed of dark matter — but instead discovered the largest Ly-alpha Nebula ever seen and possibly the first image of an intergalactic cosmic web filament. A discovery of this magnitude not only gave them answers, but also opened grounds for further questions and research.
“On one side, this image confirms a long-standing picture of structure and galaxy formation in the universe that so far was only visible in [computer] simulations,” Cantalupo said. “On the other hand, it provides a new laboratory to test our knowledge of intergalactic gas and galaxy formation, showing how limited our understanding is of physical processes on these scales.”
The Keck Cosmic Web Imager (KCWI), designed for cosmic web research, is an upcoming addition to the Keck Observatory. This instrument will be completed next year, and will allow researchers to observe the movement, abundance and chemical makeup of other structures similar to Slug Nebula.
“I’m switching over to working with Professor Prochaska on quasar absorption spectroscopy,” said astronomy and astrophysics graduate student Camille Leibler. “Given that the KCWI will come online during my grad school career, this is the sort of research I’d be very excited to work on.”
UCSC’s astronomy and astrophysics department is already the second most prestigious one in the country, said Anne L. Kenney of the Cornell University Library in a press release. This major discovery by Cantalupo and his research team will pave the way for future students and researchers interested in the cosmic web structure.
“This discovery was a dream that we thought was not possible to realize yet with our current instruments,” Cantalupo said. “Like many other discoveries, it took time, patience and a bit of luck, of course.”