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The following is an extract from our聽Lost in Space-Time聽newsletter. Each month, we dive into fascinating ideas from around the universe. You can聽sign up for聽Lost in Space-Time听丑别谤别.

On 30 August, NASA launched its latest flagship space observatory, the Nancy Grace Roman Space Telescope. It is an incredible piece of technology: it is the same size as the Hubble Space Telescope but with a far broader field of view. Over the course of its five-year primary mission, Roman is expected to observe about 12 per cent of the sky in incredible detail, peering into the distant reaches of the universe. It doesn鈥檛 sound like a lot, but that鈥檚 a giant leap from its predecessors 鈥� Hubble observed only 0.1 per cent of the sky over 35 years.

This wider view will allow Roman to catch cosmic events as they evolve in real time, and observe an astounding variety of both new and already-known objects in space. But the pi猫ce de r茅sistance will be what it can do for our studies of dark matter and dark energy, the mysterious stuff that makes up about 95 per cent of the universe. Indirect observations tell us that both of these enigmatic components of the cosmos exist, but we know little to nothing about what they actually are or how they work. Roman may be the key that finally unlocks some of their mysteries.

Roman鈥檚 powerful 300-megapixel camera was activated two weeks after launch, opening its eyes to the universe as part of the telescope鈥檚 commissioning process. The first photons of starlight it took in created fuzzy green rings, an expanse of out-of-focus stars. Kristen McQuinn, a professor at Rutgers University in New Jersey and the head of the Space Telescope Science Institute鈥檚 Nancy Grace Roman Space Telescope mission office, tells me this is only the beginning. The next steps are to focus the camera, turn on the guidance systems and find out what astonishing things this new observatory will teach us about the universe.

Leah Crane: So, first things first: how was it to finally see that first image?

Kristen McQuinn: It鈥檚 extremely intense. The teams are on duty 24/7, so there are a lot of people on shifts around the clock. These first images were taken in the middle of the night, but the run-up to this had been going so incredibly well. Leading up to this, we鈥檙e all kind of on a high. For the test image, the telescope hasn鈥檛 been focused yet, and the telescope is also not guiding yet 鈥� the telescope is pretty stable when you point it at something, but it can drift a little bit. The test image didn鈥檛 have the guiding and it was unfocused, and even with that, the image is really spectacular. The lack of focus is really not more than was expected from launch and all of the stressors that come with the launch of a telescope into space: it鈥檚 telling us that we鈥檙e in really good shape. The image is so full of promise 鈥� everybody is so excited.

Normally, when we get a big new observatory, it鈥檚 either bigger than the previous ones, or it鈥檚 observing in a unique wavelength of light that we didn鈥檛 have coverage of before, but Roman isn鈥檛 either of those things. I don鈥檛 want to be disrespectful here, but given that, why have we put so much work and investment into it?

No offense taken at all! It鈥檚 got a mirror similar to Hubble鈥檚 in size, and it covers some wavelengths that are also overlapping with Hubble and the James Webb Space Telescope, so why do it? The difference with Roman is how much of the sky it can see all at once, its field of view. Hubble and Webb are like a zoom lens on your camera, but Roman is like a panoramic picture. It sees about 100 times larger than the field of Hubble, but it鈥檚 built in such a way that it can map areas of the sky about 1000 times as fast as Hubble. Every 10 months, we are going to get the equivalent of about 1000 years of Hubble observations.

From a usage standpoint, it鈥檚 very different. Because Roman can see large areas of the sky, that鈥檚 what we鈥檙e going to do. That鈥檚 why some of the biggest science goals for Roman are understanding dark energy and dark matter, because to probe both of those you need really, really wide areas of the sky to explore.

How is it that Roman is so much faster than Hubble despite their primary mirrors being the same size?

The actual detector is much larger, and it鈥檚 positioned in this unique shape. The way Roman is designed, it captures the light in the big primary mirror and it focuses it onto the detector, and because of advances in technology since Hubble was launched in 1990, Roman can bring a larger area into focus. It can also move and map the sky faster than Hubble because of the way that it鈥檚 built. Its structure is much lighter, less than a quarter of the weight of Hubble. It鈥檚 also built with a stiffer integrity, and that means that it鈥檚 got this ability to have rapid torques over short distances. So, you have this stiff, light structure that can pivot and then still itself really, really quickly. You鈥檙e able to get a bigger field of view, and then you can move the thing between fields of view much, much faster.

Why is getting such a huge field of view important?

There鈥檚 this term, cosmic variance, and it says that the universe is, on very large scales, pretty homogeneous. So, if you look at one big area of the universe, it might be similar to all the others, but when you zoom in on any smaller area, everything is different and there are lots of unique things there. So, with Hubble and Webb and other telescopes with smaller fields of view, you can鈥檛 really know if you鈥檙e studying unique areas of the universe. Because of this cosmic variance, you need to zoom out to larger areas in the sky to know whether or not what you鈥檙e seeing is representative of the universe. A bigger field of view allows you to get out of this cosmic variance problem.

How does that field of view help with your research?

My own research is on small galaxies 鈥� the smaller, the more interesting they are to me, because they鈥檙e very sensitive to all kinds of dark matter physics and physics of the conditions of the early universe and things that are otherwise hard to probe. With Roman, it鈥檚 going to be like a galaxy-hunting machine for these small galaxies.

Because these galaxies are so small, they have very shallow gravitational potential wells [meaning that they don鈥檛 have much mass, and it isn鈥檛 particularly tightly bound together]. And because they have shallow gravitational potential wells, they are more susceptible to what happened in the early universe, especially during the epoch of reionisation, when copious amounts of UV radiation were produced by massive stars. There鈥檚 a lot of tie-in between the properties of these galaxies and reionisation physics, and that鈥檚 tied to dark matter physics because the gravitational potential is set by the amount of dark matter.

So that鈥檚 one way Roman tells us about dark matter, but it seems pretty indirect to me. Are there more direct ways, too?

One of the things Roman is going to measure is weak gravitational lensing [where a massive object in the foreground of an image warps the light coming from objects behind it, allowing us to detect and map the relatively nearby mass even if we can鈥檛 see it directly]. Through that, you are able to measure the clustering and the shape of galaxies being affected by dark matter and dark energy, across the span of time. The weak lensing measurements for Roman are going to be exquisite, because some of the most stringent requirements on the design of the telescope are related to making this weak lensing measurement. It鈥檚 a really hard measurement to make, but Roman will be one of the most precisely, if not the most precisely, calibrated telescopes ever.

Do Roman鈥檚 dark-matter-measuring abilities tie in at all with what鈥檚 happening in laboratories and astroparticle observatories right now, as they鈥檙e investigating the possibility of a dark matter particle detection?

Yes! The clustering of galaxies changes if you have different dark matter particles, or the nature of dark matter is different. And by being able to measure this so exquisitely with Roman, it can help constrain or narrow down some of the dark matter candidates. If you鈥檝e got a lighter, warmer dark matter particle, then the clustering of galaxies is not quite so compact, and if you have a colder or heavier particle, then the clustering of galaxies is slightly more compact. But it鈥檚 a very subtle effect, so that鈥檚 why you need to build a telescope like Roman to do it.

As exciting as that is, dark energy is really more of the main target for Roman, right? And that鈥檚 a little more complicated than dark matter, because it鈥檚 something that鈥檚 making the whole universe expand, not a substance that is localised in one place. So aside from the lensing, how are we going to study that?

One way we measure the expansion of the universe is through type Ia supernovae explosions. These are very predictable in the way the light from their explosions changes with time, the brightness and their characteristics, which is why we call them 鈥渟tandard candles鈥�. And so, because of that, if you see one go off and you take the right observations, you can figure out how far away it is. Couple that with the velocity of the galaxy hosting the supernova explosion, and you can really start mapping out how the universe is moving over large scales.

But the capabilities that we have today can really measure supernovae out only to a certain distance, and after that, we don鈥檛 really have those capabilities. But Roman brings those capabilities, so now we can actually measure type of supernova, out through very far cosmic distances, and have one single method with one type of observatory without a lot of systematic uncertainties to be able to measure the expansion rate of the universe. That can help us understand the acceleration and whether it has changed at different epochs of time.

The other way it does that is by measuring baryonic acoustic oscillations, which are these sound waves that got frozen into the universe at very early times. These are more of a standard ruler technique [because we know what size they ought to be, so by measuring the size that they appear, we can tell their distance]. And Roman will be able to study the acceleration in dark energy based on that as well.

The big question, I think, is: will Roman finally answer the question of what dark matter and dark energy really are, or is it just one more step on a long road towards the answer?

I think Roman is going to bring us new insights into these big questions. I sincerely do. It鈥檚 difficult to predict exactly the level of breakthrough, but we鈥檝e never had anything like Roman before. There are other surveys, and we鈥檙e going to learn important things from all of them in different ways. Roman isn鈥檛 the only game in town.

But it鈥檚 the newest game in town.

It is the newest game in town. And I鈥檓 a little biased, but it鈥檚 the best game in town. I think Roman is going to bring us deep insights into the nature of particularly dark energy, but also dark matter, and I think we鈥檙e going to learn a lot. Will it completely unravel all of the mysteries associated with these phenomena? Unlikely. You know, the universe is a very complex and amazing place, and the more we learn, the more we know there鈥檚 more to learn. But I think Roman isn鈥檛 just one step on a long road. We are going to get some breakthrough discoveries with the Roman observations.

The future of space travel

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