Seven billion years ago, the universe’s star formation boom began to slow. What did our Milky Way galaxy look like at that time? Astronomers using the NASA/ESA/CSA James Webb Space Telescope have discovered a clue in the form of a cosmic question mark, the result of an unusual alignment in space spanning several light-years.

“There are only three or four known examples of similar gravitational lensing configurations in the observable universe, so this discovery is exciting as it demonstrates the power of Webb and suggests that we may find more like it in the future,” said Dr Guillaume Despres, from St Mary’s University.

The region has previously been observed by the NASA/ESA Hubble Space Telescope, but Webb was the first to spot the dusty red galaxy forming an intriguing question mark shape.

This is because the wavelengths of light that Hubble detects are trapped in space dust, while longer wavelengths of infrared light pass through Webb’s instruments and can be detected.

Astronomers used both telescopes to observe the galaxy cluster. MACS-J0417.5-1154The cluster is so large that it distorts the fabric of space-time, acting like a magnifying glass.

This will allow astronomers to see clearer details of the much more distant galaxies behind the cluster.

But the same gravitational effects that expand galaxies also cause distortions, which can result in galaxies appearing spread out in an arc across the sky, or appearing multiple times.

This optical illusion in space is called gravitational lensing.

The red galaxy Webb uncovered, along with the spiral galaxy it interacts with, previously detected by Hubble, is magnified and distorted in an unusual way that requires a special and rare alignment between the distant galaxy, the lens, and the observer — something astronomers call hyperbolic umbilical gravitational lensing.

This explains five images of the galaxy pair seen in the Webb image, four of which trace the top of the question mark.

The question mark points are, from our perspective, unrelated galaxies that happen to be in the right place and spacetime.

In addition to developing a case study for Webb, Niris Noting the ability of their infrared imaging device and slitless spectrometer to detect star formation locations in galaxies billions of light years away, the research team also couldn’t help but notice the shape of the question mark.

“This is really cool. I got interested in astronomy when I was younger because I saw amazing images like this,” said Dr Marcin Sawicki, also from Saint Mary’s University.

“Knowing when, where and how star formation occurs in galaxies is crucial to understanding how galaxies have evolved throughout the history of the universe,” said Dr Vicente Estrada Carpenter from Saint Mary’s University.

“The results show that star formation is widespread in both. The spectral data also confirm that the newly discovered dusty galaxy is located at the same distance as the frontal spiral galaxy, suggesting that the two are probably starting to interact.”

“Both galaxies in the question mark pair show several dense regions of active star formation, likely the result of the gas in the two galaxies colliding.”

“But neither galaxy seems particularly disturbed, so perhaps we are seeing the beginning of an interaction.”

“These galaxies, seen billions of years ago when star formation was at its peak, are similar in mass to the Milky Way at that time,” Dr Sawicki said.

“Thanks to Webb, we can now study what our galaxy was like in its teenage years.”

Team paper Published in Monthly Bulletin of the Royal Astronomical Society.

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Vicente Estrada Carpenter others2024. CANUCS JWST/NIRISS We will use grism spectroscopy to investigate when, where and how star formation occurs in a pair of galaxies at cosmic noon. MNRAS 532 (1): 577-591; doi: 10.1093/mnras/stae1368

This article is based on a press release provided by NASA.