It’s 7 billion years ago, and the Universe’s heyday of star formation is beginning to slow. What might our Milky Way Galaxy have looked like at that time? Astronomers using the NASA/ESA/CSA James Webb Space Telescope have found clues in the form of a cosmic question mark, the result of a rare alignment across light-years of space.
The galaxy cluster MACS-J0417.5-1154 is so massive it is warping the fabric of space-time and distorting the appearance of galaxies behind it, an effect known as gravitational lensing. This natural phenomenon magnifies distant galaxies and can also make them appear in an image multiple times, as Webb saw here. Two distant, interacting galaxies — a face-on spiral and a dusty red galaxy seen from the side — appear multiple times, tracing a familiar shape across the sky. Active star formation, and the face-on galaxy’s remarkably intact spiral shape, indicate that these galaxies’ interaction is just beginning. Image credit: NASA / ESA / CSA / STScI / V. Estrada-Carpenter, Saint Mary’s University.
“We know of only three or four occurrences of similar gravitational lens configurations in the observable universe, which makes this find exciting, as it demonstrates the power of Webb and suggests maybe now we will find more of these,” said Dr. Guillaume Desprez of Saint Mary’s University.
While this region has been observed previously with the NASA/ESA Hubble Space Telescope, the dusty red galaxy that forms the intriguing question-mark shape only came into view with Webb.
This is a result of the wavelengths of light that Hubble detects getting trapped in cosmic dust, while longer wavelengths of infrared light are able to pass through and be detected by Webb’s instruments.
Astronomers used both telescopes to observe the galaxy cluster MACS-J0417.5-1154, which acts like a magnifying glass because the cluster is so massive it warps the fabric of space-time.
This allows astronomers to see enhanced detail in much more distant galaxies behind the cluster.
However, the same gravitational effects that magnify the galaxies also cause distortion, resulting in galaxies that appear smeared across the sky in arcs and even appear multiple times.
These optical illusions in space are called gravitational lensing.
The red galaxy revealed by Webb, along with a spiral galaxy it is interacting with that was previously detected by Hubble, are being magnified and distorted in an unusual way, which requires a particular, rare alignment between the distant galaxies, the lens, and the observer — something astronomers call a hyperbolic umbilic gravitational lens.
This accounts for the five images of the galaxy pair seen in Webb’s image, four of which trace the top of the question mark.
The dot of the question mark is an unrelated galaxy that happens to be in the right place and space-time, from our perspective.
In addition to producing a case study of Webb’s NIRISS (Near-Infrared Imager and Slitless Spectrograph) instrument’s ability to detect star formation locations within a galaxy billions of light-years away, the research team also couldn’t resist highlighting the question mark shape.
“This is just cool looking. Amazing images like this are why I got into astronomy when I was young,” said Dr. Marcin Sawicki, also from Saint Mary’s University.
“Knowing when, where, and how star formation occurs within galaxies is crucial to understanding how galaxies have evolved over the history of the Universe,” said Dr. Vicente Estrada-Carpenter of Saint Mary’s University.
“The results show that star formation is widespread in both. The spectral data also confirmed that the newfound dusty galaxy is located at the same distance as the face-on spiral galaxy, and they are likely beginning to interact.”
“Both galaxies in the Question Mark Pair show active star formation in several compact regions, likely a result of gas from the two galaxies colliding.”
“However, neither galaxy’s shape appears too disrupted, so we are probably seeing the beginning of their interaction with each other.”
“These galaxies, seen billions of years ago when star formation was at its peak, are similar to the mass that the Milky Way galaxy would have been at that time,” Dr. Sawicki said.
“Webb is allowing us to study what the teenage years of our own galaxy would have been like.”
The team’s paper was published in the Monthly Notices of the Royal Astronomical Society.
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Vicente Estrada-Carpenter et al. 2024. When, where, and how star formation happens in a galaxy pair at cosmic noon using CANUCS JWST/NIRISS grism spectroscopy. MNRAS 532 (1): 577-591; doi: 10.1093/mnras/stae1368
This article is based on a press-release provided by NASA.
