When the James Webb Space Telescope (JWST) began science operations, one of its first tasks was to observe the earliest galaxies in the Universe. These observations revealed a huge population of active galactic nuclei (AGNs) that astronomers nicknamed “Little Red Dots” (LRDs), owing to their small appearance and deep red hue. Based on redshift measurements, these AGNs are estimated to have existed just 0.6 to 1.6 billion years after the Big Bang (13.2 to 12.2 billion years ago). Studying these objects has already triggered some groundbreaking discoveries about the early Universe.
This includes new insights into how supermassive black holes (SMBHs) formed shortly after the Big Bang and how Dark Matter may have influenced the formation of early galaxies. Thanks to a new set of images taken with Webb’s Mid-Infrared Imager (MIRI), the JWST has now provided the first long-wavelength infrared light observations of the Hubble Ultra Deep Field (HUDF), which contains several LRDs. As an international team of researchers explained in a study published in Astronomy & Astrophysics, these images provide new insights into how the earliest galaxies in the Universe formed over 13 billion years ago.
The study was conducted by researchers with the MIRI European Consortium, an international organization made up of thousands of astronomers from institutions like the Max-Planck-Institute for Astronomy (MPIA) and the MPI for Radioastronomy (MPIfR), the Centro de Astrobiología (CAB), the Cosmic Dawn Center (DAWN), the Niels Bohr Institute (DARK), the Centre for Extragalactic Astronomy, the Kapteyn Astronomical Institute, the Institute of Particle Physics and Astrophysics, the UK Astronomy Technology Center, the Space Telescope Science Institute (STScI), and the European Space Agency (ESA).
This image combines data from the JWST’s MIRI and NIRcam cameras to create a multicoloured view of the Hubble Ultra Deep Field. Credits: NASA/ESA/CSA/the JADES Collaboration/the MIDIS collaboration.
The research was conducted as part of the MIRI Deep Imaging Survey (MIDIS), an observation campaign that revisited the iconic Hubble Ultra Deep Field (HUDFD). This survey observed the HUDFD for nearly 100 hours, Webb’s longest observation of an extragalactic field with one filter to date. These observations revealed vital information on how and when stars in the earliest galaxies form, where previous observations only measured the light of newborn stars in these galaxies.
Göran Östlin, a Professor of Astronomy at Stockholm University and the lead author on the study, explained in an ESA press release:
In the images, we can see the most distant galaxies known to us. What is unique about our observations is that they are made in mid-wavelength infrared light and with an extremely long exposure time, close to 100 hours. This allows us to study extremely distant galaxies. They emitted their light more than 13 billion years ago, near the beginning of the Universe.
For their research, the team examined the MIRI data to obtain photometry and redshifts of about 2,500 light sources, the overwhelming majority of which were distant galaxies. This data could lead to estimates on the number of stars that formed shortly after the Big Bang, allowing astronomers to study how the first galaxies in the Universe evolved. It could also enable researchers to study galaxies that contain large amounts of interstellar dust (aka. “dusty galaxies”), which could contain the seeds of SMBHs and are only visible in infrared light.
These findings could help settle questions regarding how these galaxies and their central black holes grew to their observed sizes so soon after the Big Bang. When astronomers first viewed these galaxies, they found that the observations were in tension with what the most widely accepted cosmological models predicted. These models suggested that early galaxies and the seeds of SMBHs would not have had enough time to grow to their observed sizes. In this respect, Webb’s observations have triggered a revolutionary shift in what we think we know about the birth of galaxies and cosmic structures.
Jens Melinder, an astronomer at Stockholm University and a co-author on the paper, states that these latest findings will shed light on this and other cosmological mysteries:
MIRI allows us to see through the veil of dust and observe what lies behind. By observing this type of galaxy, we can understand how quickly the heavier elements that the dust is made from formed in the early Universe, and how supermassive black holes, surrounded by a ring of hot dust, evolved. We have contributed brand new data that will be used in the future by researchers studying galaxy evolution and the formation of the first galaxies. The HUDF is such an incredibly well-observed part of the night sky that there is great value in making our images available. We expect them to be used by many.
Further Reading: Stockholm University, Astronomy & Astrophysics