by NASA’s upcoming Nancy Grace Roman Telescope could use the ugly deaths of stars torn apart by black holes to hunt for the first population of stellar bodies in the universe.
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 was not yet filled with “metals,” which astronomers use to describe elements heavier than hydrogen and helium.
Pop III stars arose just a few hundred million years after the Big Bang and were “poor metal,” composed mostly of hydrogen and helium. They were also believed to be much larger and hotter than the sun. This means that Pop III has burned through its fuel for nuclear fusion faster than smaller stars, and the short lifetimes make them targets for astronomers.
Because these earliest stars are responsible for creating metals that would form the building blocks of the next generation of metal-poor stars, studying them is critical to understanding cosmic evolution. New research suggests that the Nancy Grace Roman Telescope (or Roman for short), due to launch in 2027, may have a unique way of doing this.
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Instead of looking for intact Pop III stars, the Romans will search for what’s left of them after they’ve strayed too close to black holes and been destroyed in what astronomers call tidal disruption events, or TDEs.
“Since we know that black holes are likely to exist at these early ages, catching them eating these early stars might give us our best shot at getting Pop III stars indirect detection,” study team member and Yale University scientist Priyamvada Natarajan said in a statement.
Roman will see the destruction of the first stars
When a star passes close to a black hole, its massive gravitational pull generates enormous tidal forces within it. This causes the star to be compressed horizontally and stretched vertically. The material that makes up the star is transformed into a “noodle” of star matter, in a process called “spaghettification.”
However, the material that contained the doomed star cannot immediately fall into the black hole. Instead, it collects in a flattened cloud around the black hole called an accretion disk. As this matter passes by and towards the black hole, it rises, emitting a glow that can be seen in some cases over billions of light years.
TDEs themselves are transient events. This means that as the star is destroyed, there is a brief but intense flare in X-ray, radio, ultraviolet and optical wavelengths of light. This is how TDEs appear in the local universe, where Pop III stars no longer exist. But these violent events look very different when seen across vast distances of 13 billion light years or so.
That’s because, as light travels from these events, the expansion of space causes its wavelength to lengthen, pushing it into the infrared part of the spectrum—a phenomenon known as “redshift.”
Furthermore, the transient nature of TDEs changes as their light travels across the cosmos. This is because the redshift on TDE that brightly destroys Pop III arises over hundreds to thousands of days and fades over timescales as long as a decade.
“The evolution timescales of Pop III TDEs are very long, which is one feature that may distinguish Pop III TDEs from other transients, including supernovas and TDEs of current-generation stars like our sun,” said study team leader Rudrani Kar Chowdhury, a postdoctoral fellow at the University of Hong Kong.
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By providing a panoramic field of view of the cosmos that is 200 times greater than that provided by the Hubble Space Telescope, and by surveying the sky 1,000 times faster than this ion telescope, the Roman should be the ideal instrument to find these early TDEs, a team. members said.
Although NASA’s James Webb Space Telescope (JWST) has the kind of power that would be needed to see the distant and early TDEs, its field of view is also much smaller than the Roman field of view. . That means it is not as effective a TDE hunter as the upcoming space telescope. The Rome High Latitude Wide Area Survey, which will have a 2,000-square-foot view of the sky beyond the plane of the Milky Way, will be especially promising in the search for destroyed Pop III stars.
“Roman 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. msgstr “That’s what’s needed to detect a meaningful sample of these TDEs.”
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That does not mean that JWST will not play a role in the search for TDEs associated with Pop III stars. When the Romans see such an occurrence, JWST’s powerful infrared sight will be able to zoom in on it and use its spectroscopic instruments to determine the presence of metals. This will determine if the TDE involves the destruction of the Pop III star.
“Since these stars are only composed of hydrogen and helium, we will not see any metal lines in the spectra of the objects, but, in the TDE spectra from regular stars, we can see different metal lines,” said Kar Chowdhury.
This tag team of Roman and JWST could therefore unlock the secrets of the earliest stars in the universe and how they influenced the evolution of the next generations of stars and the galaxies that host them.
The research was published online May 8 in the Astrophysical Journal Letters.
