The James Webb Space Telescope, the largest and most sensitive of its kind, will allow us to detect the first galaxies, says Tufts astronomer
With the goal of peering into the universe’s deep past, the James Webb Space Telescope (JWST) was launched into space six months ago. Located about a million miles from Earth, it is now fully operational after months of testing. NASA last night released the first images taken by the JWST, a 20-year project of NASA, the European Space Agency, the Canadian Space Agency, and hundreds of universities and other organizations.
The JWST, the most sensitive telescope ever commissioned, “will study every phase of cosmic history—from within our solar system to the most distant observable galaxies in the early universe,” according to NASA.
The JWST’s mirror for capturing light is over 21 feet in diameter, about 270 square feet; it was folded like origami to fit into the rocket that took it to its orbit location. To operate correctly, the telescope needs to be chilled to about -380 degrees Fahrenheit—it even has a sun shelter umbrella that is the size of a tennis court.
According to NASA, the JWST “will directly observe a part of space and time never seen before,” when the very first stars and galaxies formed more than 13.5 billion years ago.
To learn more about this groundbreaking space telescope, Tufts Now talked with Danilo Marchesini, professor of physics and astronomy, who has research projects scheduled to run on the JWST. He and Tufts colleague Anna Sajina are part of the team developing the Prime Focus Spectrograph (PFS) telescope in Hawaii, due to come online next year.
Tufts Now: What makes the JWST different from other major telescopes, from land-based ones like the PFS to the Hubble Space Telescope?
Danilo Marchesini: It is the largest space-based telescope built so far. The larger mirror means more light can be collected and so we can see fainter objects. Being almost three times larger than the Hubble Space Telescope means it can see objects almost nine times fainter—hence, being able to see more distant objects.
The larger mirror also means better image quality. The biggest advantage is that it is an infrared telescope, able to view from around 1 micron and longer wavelengths, so we can probe more distant objects. By comparison, the PFS telescope in Hawaii is optimized for collecting spectra over a very large area in the sky, but it does not go as deep, and it won’t reach as red wavelengths as JWST.
Going into space allows us to push to longer wavelengths. JWST, being an infrared telescope, is more similar to the Spitzer Space Telescope, but Spitzer is almost eight times smaller in diameter, meaning JWST will allow us to observe objects 60 times fainter and also with much better image quality.
What do you expect will be some of the questions in astronomy that the JWST will shed light on?
It will allow us to detect the first galaxies, and to build a more complete census of the galaxy populations during cosmic history, being able to probe much fainter and much lower-mass galaxies.
It will also let us measure much more robustly how active star formation is in distinct galaxies. That’s because JWST, being able to look more into the infrared, will deliver star-formation rate measurements less affected by dust obscuration.
JWST allows us to track, for the first time, the buildup of the population of quiescent—no longer star forming—galaxies from their very first appearance. Right now, we don’t know when that happened. And it will allow us to do much more.
I understand that the JWST can “see” more in the infrared dimension than Hubble—why is that important? And can you explain what seeing in infrared means?
Seeing in the infrared means being able to measure the light at wavelengths longer than our eye can see. This is important because the more distant a galaxy is, the faster it is moving away from us, because of the expansion of the universe. The faster away an object is moving, the more its spectrum—the light that it emits—is shifted to longer wavelengths.
So, while we can observe galaxies that are around us in the local universe in the optical or visible light, as we move to more distant galaxies, we need to be able to observe light at progressively longer wavelengths to be able to make similar measurements.
But from the ground we are limited to wavelengths below 2.5 microns. To go beyond that, which we need to do to study in greater detail the most distant galaxies, we need to go into space. The problem of moving into space with an infrared telescope is that you need the telescope and instruments to be cold—very cold—to observe in the infrared. Cooling requires either a lot of coolant liquid, which is heavy and it runs out, or some clever way like the passive cooling system on JWST.
Do you have projects on the JWST? If so, can you give some details about them and their goals, and when you hope to have the data?
I am closely involved in five awarded programs and am very excited about all of them.
One is an early release study program, and we are expecting to receive the first big chunk of data as soon as July 13. We have spent the last many months getting ready for it, to take advantage of the data as soon as they are released. It’s going to be a very intense month ahead.
One program I am very closely involved with is going to target three candidates of very massive galaxies from when the universe was only 1 billion years old that are no longer forming stars. Current state-of-the-art theoretical models are not able to explain the existence of such systems.
This JWST program will be taking images and spectra of these three targets to spectroscopically confirm their distance, their quiescent nature, and measure other properties like the level of star formation, star formation history, and presence of an actively accreting super-massive black hole.
Another program aims at obtaining a complete view of cosmic star formation across the majority of cosmic history.