NASA’s upcoming Nancy Grace Roman Telescope could use the grisly death of stars being torn apart by black holes to hunt for the universe’s first population of stellar bodies.
These early stars, referred to (somewhat confusingly) as Population III (Pop III) stars, were very different from the sun and other stars seen in the cosmos today. That’s because the universe wasn’t yet full of “metals,” a term astronomers use to describe elements heavier than hydrogen and helium.
Pop III stars emerged only a few hundred million years after the Big Bang and were “metal-poor”, consisting mostly of hydrogen and helium. They were also believed to be much larger and hotter than the sun. This means Pop IIIs consume nuclear fusion fuel faster than smaller stars, and these short lifetimes make them elusive targets for astronomers.
Because these early stars were responsible for forging metals that would become the building blocks of future generations of less metal-poor stars, studying them is key to understanding cosmic evolution. New research suggests that the Nancy Grace Rome Telescope (or Roman for short), scheduled to launch in 2027, may have a unique way of doing this.
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Instead of searching for pristine Pop III stars, Roman will search for what’s left of them after they come too close to black holes and are destroyed in what astronomers call tidal disruption events, or TDEs.
“Since we know that black holes likely existed in these early periods, capturing these early stars as they swallowed them may offer us the best chance of indirectly detecting Pop III stars,” said study team member and Yale University scientist Priyamvada Natarajan. expression.
Roman will watch the first stars disappear
When a star passes near a black hole, the enormous gravitational pull it encounters creates enormous tidal forces within it. This causes the star to be stretched vertically and compressed horizontally. The material that makes up the star is transformed into a “noodle” of star matter in a process called “spaghettification”.
However, the matter that once formed the star that was doomed to disappear cannot immediately fall into the black hole. Instead, it collects in a flattened cloud around the black hole called the accretion disk. As this material spirals around and towards the black hole, it heats up and in some cases emits a glow that can be seen billions of light years away.
TDEs themselves are transient events. This means that as the star is destroyed, a brief but intense flash occurs in X-ray, radio, ultraviolet and optical light wavelengths. This is how TDEs arise in the local universe where Pop III stars no longer exist. But these violent events look quite different when viewed from distances as wide as 13 billion light-years.
This is because as the light from these events progresses, the expansion of space causes the wavelength to lengthen, pushing it towards the infrared part of the spectrum; This phenomenon is called “redshift”.
Additionally, the transient nature of TDEs changes as their light moves through the cosmos. This is because the redshift causes a Pop III-destroying TDE to glow for hundreds to thousands of days and then dim for as long as a decade.
“The evolution timelines of Pop III TDEs are very long, a feature that may distinguish Pop III TDE from other transient events, including supernovae and TDEs of current generations of stars such as our sun,” study team leader Rudrani Kar Chowdhury said. Postdoctoral researcher at the University of Hong Kong.
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Providing a panoramic view of the cosmos 200 times larger than that provided by the Hubble Space Telescope and scanning the sky 1000 times faster than this ionic telescope, Roman should be an ideal tool for finding these first TDEs. members said.
While NASA’s James Webb Space Telescope (JWST) has the power needed to see these distant, early TDEs, its field of view is also much smaller than Roman’s. This means it is not as effective a TDE hunter as the upcoming space telescope. Particularly promising in the search for destroyed Pop III stars will be Roman’s High Latitude Wide Field survey, which will have a 2,000 square degree view of the sky outside the plane of the Milky Way.
“Rome can go very deep and still cover a very large area of the sky,” said team member Jane Dai, a professor of astrophysics at the University of Hong Kong. “This is what is needed to detect a meaningful pattern of these TDEs.”
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That doesn’t mean JWST won’t play a role in the search for TDEs featuring Pop III stars. Once Roman detects such an event, JWST’s powerful infrared image will be able to zoom in on it and use its spectroscopic instruments to detect the presence of metals. This will determine whether TDE truly involves the destruction of a Pop III star.
“Since these stars consist only of hydrogen and helium, we will not see any metal lines in the spectrum of the objects, whereas we can see various metal lines in the TDE spectra of normal stars,” said Kar Chowdhury.
This team of Roman and JWST can therefore reveal the secrets of the universe’s oldest stars and how they influence the evolution of future generations of stars and the galaxies that host them.
The research was published online May 8 in the journal Astrophysical Journal Letters.