What was the universe like in the first few hundreds of millions of years after it came into existence? How did the first stars and galaxies form? Those are questions that astronomers now have a better chance of answering, thanks to a new research program using the James Webb Space Telescope (JWST), which came online in 2022. 

The MINERVA program, co-led by a Tufts astronomer, will give researchers an even better view than before of the early universe by using instruments on the Webb telescope that look at a different spectrum of light than usually employed. With that ability, researchers hope to find rare and unusual galaxies to help them understand galaxy formation, peer through dust to learn if some of the oldest galaxies are still creating new stars, and understand more about how supermassive black holes are formed. 

MINERVA—which stands for Medium-band Imaging with NIRCam to Explore ReVolutionary Astrophysics—started using the Webb telescope on July 25; observations are planned to run for a year. Danilo Marchesini, professor of physics and astronomy and dean of research for Arts and Sciences at Tufts, is co-principal investigator of MINERVA, which involves Tufts faculty and students as well as researchers from many universities and institutions worldwide. It is funded by NASA through the Space Telescope Science Institute.

Other powerfully sensitive telescopes, including the Hubble Space Telescope, have done similar surveys, but were unable to provide high-definition images of the very distant Universe, in the first billion year of cosmic history.

With the MINERVA project, astronomers will be obtaining medium-band imaging using the NIRCam instrument on the JWST, and also imaging from another JWST instrument called MIRI, which will allow for more fine-tuned observations of areas that were previously surveyed, especially for dust-obscured objects. 

“The idea here is to get the ultimate multi-wavelength dataset for extragalactic astronomy science,” says Marchesini. They are targeting four major extragalactic fields—meaning those outside of our own Milky Way galaxy—expecting much finer detail.

With the new data they’ll be gathering “comes very precise knowledge of the properties of those galaxies and their stellar populations—the stellar mass of the galaxy, how many stars that galaxy is forming every year, and its star formation history,” he says.

Seeing Rare Objects

With broadband imaging, scientists were able to scan large sections of the cosmos, but sacrificed focus—they couldn’t always tell if the emissions they were seeing were from fully formed stars, intense star formation, or supermassive black holes. 

But with the medium-band imaging, “we’re sampling spectral energy distribution much more finely, a factor of a few times better than with the broadband,” Marchesini says. That means, for example, they can discriminate between a galaxy that is quiescent—no longer forming stars—versus a galaxy that is actively forming a lot of stars but dust obscuration makes it appear like a quiescent galaxy with only broad-band imaging.

The four extragalactic targets that MINERVA is focusing on “will increase by a factor of about 10” the area of extragalactic fields for which astronomers will have full, in-depth sampling. 

“The area is important, because what we’re also after are rare objects,” says Marchesini. “You need to sample a larger volume of the universe to find very exciting, rare objects, especially if you go to those galaxies where they’re either the first galaxies that formed or these very exciting quiescent galaxies in the first billion years of cosmic history.”

One of the goals is to focus on the time period known as the cosmic dawn—an early phase in the growth of the universe after the Big Bang. In the first few hundred million years, the universe was made entirely of neutral hydrogen and helium, an era called the dark age. “It’s before the first stars and galaxies appeared,” says Marchesini. “Then the first stars, galaxies, and black holes appear.”

A Shift in Time

In astronomy, the more distant that objects are in space reflects how long ago in time they were formed, because the farther away an object is, the further back in time we are seeing it. That distance is measured in redshift—essentially a change in the spectrum of light emitted by an object as it travels away from us. The more distant it is, the larger its redshift is.

To observe the universe when it was 5 billion years younger —when the universe was about 7.7 billion years old—“we need to observe galaxies with a redshift value of 1, but if we want to observe galaxies when the universe was one or half a billion years old, we need to observe galaxes with a redshift value of 6 or 10,” says Marchesini.

“One of the goals of the Webb telescope is to find the first stars, the first galaxies,” he says. “With MINERVA, there’s a lot of different things that we want to find, and one is looking for very robust candidates of galaxies in the first 300 million years, or redshift above 13.”

With the medium-band imaging, astronomers can tell the difference between objects from redshift 13 and, say, much later dust-obscured galaxies from redshift 5. (Dust-obscured light is fainter, making it appear farther than it really is.) With that information, the researchers can “try to better stitch together the pieces of how galaxies evolved, especially through this dusty phase,” he says.

Researchers are also very interested in the first quiescent galaxies—galaxies that stopped forming stars and remain quiescent for the rest of their existence. “MINERVA will allow us to identify a very robust sample of quiescent galaxies all the way from redshift 3, where we know quiescent galaxies exist, to redshift 8, really trying to find when the first quiescent galaxies appear in the universe,” Marchesini says.

They will also be able to track the frequency and density of quiescent galaxies over cosmic time. “Once we know that observationally, we can then understand through simulations and models all of the interesting physical mechanisms that are responsible for their growth, their quenching, and really having a synergistic approach between observations and theory,” Marchesini says.

Another goal of MINERVA is to better understand a class of objects found earlier by Webb telescope, called “little red dots.” Astronomers think they are supermassive black holes, but don’t know whether there’s gas and stars around them. 

“MINERVA certainly will enable us to identify little red dots in a much more robust way,” says Marchesini, “pinning down the evolution of the number density of little red dots—and of the central supermassive black hole we think are generating them. This is really important to understand how, for example, supermassive black holes grew in the universe, and how they connect with the host galaxy that they live in.” 

Currently there is a wide range of theoretical models on supermassive black hole development, and Marchesini says that the little red dots “might hold the key to understand or to discriminate between those different scenarios and models.”

Marchesini says he is excited as the MINERVA program begins this summer. “It will definitely provide transformative science and results,” he says.