James Webb Space Telescope catches ‘imposter’ galaxies red-handed | Space

Dusty, star-forming galaxies that existed a billion years after the Big Bang could be masquerading as the record-breaking galaxies discovered by NASA’s new space telescope that have been thought to date to even earlier times.

In the weeks since the first batch of science data from the James Webb Space Telescope (JWST) was released, astronomers have been reporting a steady stream of candidate galaxies far more distant than any seen before the launch of NASA’s flagship space telescope. If measurements are correct, then these galaxies existed just 200–300 million years after the Big Bang, but now two independent teams of astronomers are calling at least some of them into question.

The more distant a galaxy is, the earlier in the universe we are seeing it and the more its light has been stretched by the expansion of the universe, resulting in blue and ultraviolet light from hot young stars appearing as infrared to us after traveling for over 13.5 billion years. It’s why we need the infrared capabilities of JWST to see them. Astronomers call this effect ’redshift,’ and the greater the redshift, the more distant the galaxy and the earlier in the universe’s history we are seeing it.

However, according to the two teams at least one of these galaxies, CEERS-DSFG-1, is an imposter.

Based on how red the galaxy appears to JWST, astronomers had determined a redshift of 17 to 18 for CEERS-DSFG-1, placing it just 220 million years after the Big Bang. Yet a team led by Jorge Zavala of the National Astronomical Observatory of Japan used the NOEMA (Northern Extended Millimeter Array) submillimeter telescope in France to detect this distant galaxy and find that it contains huge amounts of dust.

Dust absorbs shorter, bluer wavelengths of starlight while allowing longer, redder wavelengths to pass, meaning that a dusty galaxy can mimic the redness of a higher redshift galaxy. Once this was taken into account, Zavala’s team calculated a redshift of just 5 for CEERS-DSFG-1, placing it some 12.5 billion years ago, 1.3 billion years after the Big Bang. It’s still old and far away, but not to any record-breaking length.

Far from being bad news, discovering more galaxies at redshift 5 is actually crucial for a better understanding of how galaxies grew during that period in the history of the universe. …