On August 30, the Nancy Grace Roman Space Telescope successfully launched from Florida and will spend the next three months heading to its new home: a Sun-Earth Lagrange point, a million miles from Earth, where the gravity of the two largest bodies is in balance. It’s a comfortable place for a space telescope; Roman can say hello to his old classmate Webb, who arrived there four years ago and has been sending back brilliant images and doing good science. Roman is a strange bird by NASA standards. Arrived under budget and ahead of schedule. Its main mirror, donated by the National Reconnaissance Office, comes from a canceled spy program. There will be a trial period to make sure everything is working well, so Roman won’t officially enter service until next year. I’m sure I’ll fawn over his debut images (half of Roman’s job description is searching for new planets), but the other half is also pretty valuable. Without any hyperbole: what Roman sees could help us discover what the universe is made of and its final destiny. Great questions! I hope the brave telescope is up to the task. Saul Loeb/AFP via Getty Images First, the exoplanets. Roman: Named after Nancy Grace Roman, NASA’s first chief astronomer and “mother” of the Hubble Telescope; certainly a nobler eponym than James Webb, it is equipped with the most advanced coronagraph instrument in the world. At its most basic, a coronagraph is almost ridiculously simple: an accessory that blocks light from the star it’s pointed at, so scientists can see what’s around the star. At first, that meant the crown of our Sun. In Roman, it means those planets that revolve around other stars. These exoplanets are so dark that they are lost in the glow of the stars they orbit. The star is millions of light years from us, and its planets are only millions of kilometers from said star, so the distance between them is basically nothing from our frame of reference. Viewing them isn’t just putting a bottle cap over a lens to block the blinding starlight. Instead, Roman’s coronagraph uses a series of masks, deflectors, stops and detectors to identify and detect it. Here’s a short NASA video explaining it that even my dumbass could understand, for the most part. An especially interesting part of the coronagraph involves two flexible mirrors, driven by hundreds of tiny pistons, which shape the mirrors to serve as prisms to fit the exact wavelength of the light you’re trying to block and the light you’re trying to image. The current list of exoplanets that have been directly imaged is short, and they are mostly the same type of planets: young, bright in the infrared, far from their stars. And the images are rudimentary, often a single pixel. Roman is going to get them out of the water. You will be able to see closer planets, perhaps in the “habitable zone” of your system. You will see planets that are billions of years old, which will teach us more about planetary development outside our solar system than we have been able to learn in all of human history up to this point. You can even tell, thanks to the spectroscopic mode of your coronagraph, whether an exoplanet has clouds or an atmosphere. This time next year, we may be seeing the pale blue dot of some other star. Exoplanets are a sexy thing, because you can look at them and imagine (I love doing imaginations). The planets are easy to understand. I live in one. Dark energy, on the other hand, is almost inconceivably strange. We don’t know what it is (we have some theories). We only believe it exists because mathematics doesn’t work without it. In 1929, Edwin Hubble discovered that more distant objects move away from us faster than closer objects, proving that the universe is expanding. This was explained with the famous and widely accepted Big Bang theory. It makes sense. Big kablammo, everything blows outward, but eventually, scientists thought, the gravity of all the matter in the universe would win out and the universe would contract in a Big Crunch. But in 1998, scientists discovered that the universe’s expansion rate appears to be accelerating, not slowing down or even staying constant. How can this be? Here comes dark energy, a mysterious force, distributed more or less uniformly everywhere, and which necessarily possesses the property of negative pressure that drives the outward expansion of the universe. It explains pretty well what we see in reality, even if it’s just an “X” to balance the equations. But if we take all the normal things we can quantify (Y) and then measure how fast the universe is expanding (Z), we can subtract ZY to determine how much X there is. In the most widely accepted theory of dark energy, ordinary matter and energy (stars, galaxies, you, everything we can see) make up only five percent of the mass-energy of the observable universe. Twenty-seven percent is dark matter (which is also mysterious, but increasingly less so). The rest, 68 percent of the entire universe, has to be dark energy. However! However. In that widely accepted theory, dark energy is a constant thing: the same everywhere, all the time, which means the expansion should only increase. In recent years, observations of unfathomably distant objects (including the cosmic microwave background, the energy left over from the formation of the universe) have yielded some rather strange results. They indicate that the effect of dark energy has potentially been weakening over time. Maybe it’s not so constant after all. Maybe it’s changing. “It seems more and more that we need to modify our standard model of cosmology so that these different data sets make sense together,” said Will Percival, a professor at the University of Waterloo who is working on the Dark Energy Spectroscopic Instrument project, a ground-based collaboration of more than 900 researchers from 70 institutions, and unrelated to the Roman telescope. “And the evolution of dark energy looks promising.” This will be very important for how the universe ends. If expansion is enough, we will be facing the canyon of a Great Rip, where the universe expands so much that even the most fundamental particles end up shattered. If expansion is slowing enough to allow gravity to take over, we will have a Big Crunch. If dark energy is changing in a cyclical pattern, the universe could forever be experiencing a Big Crunch/Big Bang death and rebirth; we could simply be in one of its endless cycles. The data here is very tight. It’s possible that the confusing measurements from recent years are all within the margin of error. So how do you know if this is real? We make our measurements even more accurate. That’s where Roman comes in. Everything will be examined. Its camera is not much more powerful than Hubble’s, but its field of view is a hundred times wider. That means much less time needed to examine the sky and many more repeated studies of the same areas of the sky to see how things change over time. A new supernova brightens or dims, and Roman will detect it faster than we’ve ever been able to. A gravitationally lensed image of a distant galaxy changes its appearance for just an instant, and Roman will notice. Roman will provide the broadest, clearest, most detailed picture of the cosmos as a changing thing, and we should go some way towards understanding whether what he sees fits our current models of the universe, or whether those models need to be changed. Roman won’t do it alone. Scientists will compare their measurements with those taken from observatories working in other spectra and with different instruments: Webb, ESA’s Euclid, the ground-based Rubin, even the old and reliable Hubble, which is still working after 36 years. “Roman, Rubin and Euclid are brothers. They were all proposed and prioritized at the same time, so the design of each of those observatories was based on knowing what the others were doing,” Julie McEnery, senior scientist on Roman’s project, told Space.com. “We are not competitors. We are stronger together and we both need each other.” It’s very comforting when telescopes work together to figure out how the universe is going to die.Recommended
