A Canadian-led team has upended our notions of what some of the very first stars in the Universe looked like, and how we'll find them using the next generation of great space observatories
Scientists are on the hunt to find the first stars ever formed in our Universe, but how do they know what signs to look for? A new paper published in The Astrophysical Journal Letters provides startling new evidence that some of the first stars may have been far more massive and unusual than ever thought possible. This new knowledge acts as signposts on our roadmap to find the earliest stars in the Universe, showing us where to look and how to identify them by their colours, using the recently launched James Webb Space Telescope.
The Canadian-led paper builds on cutting-edge computer simulations of what the earliest star nurseries might have looked like. Using Blue Waters (one of the most powerful supercomputers in the world, dedicated to science and engineering research), researchers studied a "model Universe" drawn from a specialized dataset called the Renaissance suite.
Zooming in on some of the most chaotic, dense environments in this model of the early Universe, the international collaboration found primordial gas clouds in a pressure cooker. The primordial clouds could be heated to temperatures almost 100 times greater than typical in the early Universe, just from the process of merging with neighbouring gas clouds and from the light emitted by adjacent gas clouds or "halos." While stars continued to form, the heating delayed their "birth," meaning that extraordinarily massive stars, upwards of thousands of times more massive than our own Sun, were able to form.
"It turns out that the temperature of the surrounding gas in which stars form is the dial that sets the scale for how quickly stars can grow, and how massive they can ultimately become. What we see in these unique environments is the perfect nursery for raising extremely luminous, massive stars. And perhaps most significantly, this finding has resurrected hopes that at least some of the first clusters of stars will be bright enough to be detected by the next generation of telescopes."
New colour-coding for our roadmap to the early Universe
What really came as a surprise was what these first stars looked like. It has long been held on simple theoretical grounds that the first stars, though never before seen, would be very blue. In the new results, however, Dr. Woods and his team showed that many of these stars grew so rapidly, their appearances became fundamentally changed.
"As gas piles onto these forming stars, it brings in heat along with it. What we found is that many of these first stars are growing much, much faster than that heat can radiate away, so they puff up, becoming very red and bloated," Dr. Woods explains. This behaviour is unlike anything else in the early Universe, providing a unique tell-tale signature of their colour that astronomers can use as a signal pointing to where the first stars are forming within the sensitive images to come."
Finding the first stars in the Universe using the next generation of great space observatories
These predictions come at a critical time because astronomers have made finding the first stars a top priority for the next decade. The first stars are the key to unlocking the mysteries underlying everything from the nature of the first black holes, to the formation of galaxies, and to the origin of the elements in the Periodic Table. Since light travels at a fixed speed, looking farther away we see the Universe earlier in its history. With this in mind, the next great observatories are all aiming to look deeper into the faint and distant early Universe than ever before.
Such observations are indeed a key goal of the James Webb Space Telescope (Webb), the much-anticipated successor to the Hubble Space Telescope.
"The James Webb Space Telescope will look at several patches of sky for days at a time, to detect and identify the most distant stars and galaxies. Two planned surveys in particular will be essential in this search: one, the JADES survey (James Webb Space Telescope Advanced Deep Extragalactic Survey) will look at 2 previously well-studied fields in the largest program performed in the first year of Webb's operations, while the CANUCS survey (Canadian NIRISS Unbiased Cluster Survey) will harness magnification by foreground galaxy clusters to amplify the light from extremely faint distant stars and galaxies. These new predictions will guide those teams to be on the lookout for first stars that may be very red and not just blue, as previously expected."
Now armed with the means to spot these first, enormous stars in the early Universe, astronomers will soon unlock the mysteries of their origin, and determine their profound impact on the subsequent evolution of the Cosmos.