Signs of low-mass first-generation stars have appeared to be more plentiful in their descendants, which contain large amounts of carbon and other light elements, but until these results, scientists had detected no traces of their very massive siblings. The scarcity suggested that low-mass stars were more numerous in the early universe.
"We have come to understand that the first stars had a range of masses, from a few solar masses, all the way up to 100 solar masses, or even more," Bromm told Space.com via email. "The typical, or average, mass is predicted to be somewhere close to a few tens of solar masses.".
Massive stars burn through their material far faster than their lower-mass relations. Therefore, no high-mass stars should exist today. But Aoki suggested that smaller ones could still be visible.
"In the Milky Way, low-mass Population III stars, which have sufficiently long lifetimes, can be found if they have formed at all," he said.
Such stars would be difficult to detect. According to Bromm, their radiation would have been shifted by the expanding universe into the near-infrared wavelength, which requires sensitive space-based detectors.
"This is one of the main targets for [NASA's] James Webb Space Telescope (JWST), planned for launch in 2018," Bromm said.
More massive stars, such as the one that preceded SDS J10018, would be short-lived, so scientists would have to search back to the early universe. Because distance and time are related — observing a star that is 13 billion years old requires looking out a distance of 13 billion light-years — the search would require a massive and extraordinarily sensitive telescope, such as the upcoming Thirty-Meter Telescope and the Giant Magellan Telescope.
In addition to detecting early stars, JWST should also be able to detect the supernovas that mark the end of their lifetimes, Bromm said.
Detecting the material left behind would be more difficult. Due to their low content of heavy metals, early supermassive stars experienced a different type of supernova than stars do today. Those huge stars that undergo the standard core collapse supernova explosion would leave behind enormous black holes that could have formed the seeds of the supermassive black holes that lie at the centers of galaxies. These black holes, along with the neutron stars that could have also formed, would be a challenge to detect.
Aoki expects to continue detailed studies of the evolution and explosion of extremely massive stars.
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