Primordial Asteroids Discovered

Southwest Research Institute (SwRI) was part of an international team that recently discovered a relatively unpopulated region of the main asteroid belt, where the few asteroids present are likely pristine relics from early in solar system history. The team used a new search technique that also identified the oldest known asteroid family, which extends throughout the inner region of the main asteroid belt.

The main belt contains vast numbers of irregularly shaped asteroids, also known as planetesimals, orbiting the Sun between Mars and Jupiter. As improved telescope technology finds smaller and more distant asteroids, astronomers have identified clusters of similar-looking bodies clumped in analogous orbits. These familial objects are likely fragments of catastrophic collisions between larger asteroids eons ago. Finding and studying asteroid families allows scientists to better understand the history of main belt asteroids.

“By identifying all the families in the main belt, we can figure out which asteroids have been formed by collisions and which might be some of the original members of the asteroid belt,” said SwRI Astronomer Dr. Kevin Walsh, a coauthor of the online Science paper detailing the findings. “We identified all known families and their members and discovered a gigantic void in the main belt, populated by only a handful of asteroids. These relics must be part of the original asteroid belt. That is the real prize, to know what the main belt looked like just after it formed.”

Identifying the very oldest asteroid families, those billions of years old, is challenging, because over time, a family spreads out. As asteroids rotate in orbit around the Sun, their surfaces heat up during the day and cool down at night. This creates radiation that can act as a sort of mini-thruster, causing asteroids to drift widely over time. After billions of years, family members would be almost impossible to identify, until now. The team used a novel technique, searching asteroid data from the inner region of the belt for old, dispersed families. They looked for the “edges” of families, those fragments that have drifted the furthest.

“Each family member drifts away from the center of the family in a way that depends on its size, with small guys drifting faster and further than the larger guys,” said team leader Marco Delbo, an astronomer from the Observatory of Cote d’Azur in Nice, France. “If you look for correlations of size and distance, you can see the shapes of old families.”

“The family we identified has no name, because it is not clear which asteroid is the parent,” Walsh said. “This family is so old that it appears to have formed over 4 billion years ago, before the gas giants in the outer solar system moved into their current orbits. The giant planet migration shook up the asteroid belt, removing many bodies, possibly including the parent of this family.”

The team plans to apply this new technique to the entire asteroid belt to reveal more about the history of the solar system by identifying the primordial asteroids versus fragments of collisions. This research was supported by the French National Program of Planetology and the National Science Foundation. The resulting paper, “Identification of a primordial asteroid family constrains the original planetesimal population,” appears in the August 3, 2017, online edition of Science.

Hubble Detects Exoplanet With Glowing Water Atmosphere

Scientists have found the strongest evidence to date for a stratosphere on an enormous planet outside our solar system, with an atmosphere hot enough to boil iron.

An international team of researchers, led by the University of Exeter, made the new discovery by observing glowing water molecules in the atmosphere of the exoplanet WASP-121b with NASA’s Hubble Space Telescope.
In order to study the gas giant’s stratosphere – a layer of atmosphere where temperature increases with higher altitudes – scientists used spectroscopy to analyse how the planet’s brightness changed at different wavelengths of light.

Water vapour in the planet’s atmosphere, for example, behaves in predictable ways in response to different wavelengths of light, depending on the temperature of the water. At cooler temperatures, water vapour in the planet’s upper atmosphere blocks light of specific wavelengths radiating from deeper layers towards space. But at higher temperatures, the water molecules in the upper atmosphere glow at these wavelengths instead.
The phenomenon is similar to what happens with fireworks, which get their colours from chemicals emitting light. When metallic substances are heated and vaporized, their electrons move into higher energy states. Depending on the material, these electrons will emit light at specific wavelengths as they lose energy: sodium produces orange-yellow and strontium produces red in this process, for example.

The water molecules in the atmosphere of WASP-121b similarly give off radiation as they lose energy, but it is in the form of infrared light, which the human eye is unable to detect.

The research is published in leading scientific journal Nature.

“Theoretical models have suggested that stratospheres may define a special class of ultra-hot exoplanets, with important implications for the atmospheric physics and chemistry,” said Dr Tom Evans, lead author and research fellow at the University of Exeter. “When we pointed Hubble at WASP-121b, we saw glowing water molecules, implying that the planet has a strong stratosphere.”

WASP-121b, located approximately 900 light years from Earth, is a gas giant exoplanet commonly referred to as a ‘hot Jupiter’, although with a greater mass and radius than Jupiter, making it much puffier. The exoplanet orbits its host star every 1.3 days, and is around the closest distance it could be before the star’s gravity would start ripping it apart.

This close proximity also means that the top of the atmosphere is heated to a blazing hot 2,500 degrees Celsius – the temperature at which iron exists in gas rather than solid form.

In Earth’s stratosphere, ozone traps ultraviolet radiation from the sun, which raises the temperature of this layer of atmosphere. Other solar system bodies have stratospheres, too – methane is responsible for heating in the stratospheres of Jupiter and Saturn’s moon Titan, for example. In solar system planets, the change in temperature within a stratosphere is typically less than 100 degrees Celsius. However, on WASP-121b, the temperature in the stratosphere rises by 1000 Celsius.

“We’ve measured a strong rise in the temperature of WASP-121b’s atmosphere at higher altitudes, but we don’t yet know what’s causing this dramatic heating,” says Nikolay Nikolov, co-author and research fellow at the University of Exeter. “We hope to address this mystery with upcoming observations at other wavelengths.”

Vanadium oxide and titanium oxide gases are candidate heat sources, as they strongly absorb starlight at visible wavelengths, similar to ozone absorbing UV radiation. These compounds are expected to be present in only the hottest of hot Jupiters, such as WASP-121b, as high temperatures are required to keep them in the gaseous state.

Indeed, vanadium oxide and titanium oxide are commonly seen in brown dwarfs, ‘failed stars’ that have some commonalities with exoplanets.

Previous research spanning the past decade has indicated possible evidence for stratospheres on other exoplanets, but this is the first time that glowing water molecules have been detected, the clearest signal yet for an exoplanet stratosphere.

It is one of the first results to come out of a new observing program being carried out by an international team of scientists, led by Associate Professor David Sing at the University of Exeter and Dr. Mercedes Lopez-Mórales at the Smithsonian Institution. The program has been awarded 800 hours to study and compare 20 different exoplanets, representing one of the largest time allocations for a single program in the entire 27 year history of Hubble.

“This new research is the smoking gun evidence scientists have been searching for when studying hot exoplanets. We have discovered this hot Jupiter has a stratosphere, a common feature seen in most of our solar system planets.” says Professor David Sing, co-author and Associate Professor of Astrophysics at the University of Exeter.

“It’s a truly exciting find as we’re seeing dramatic differences planet-to-planet which is giving valuable clues in figuring out how planets behave under different conditions, and we’re only just scratching the surface of all the new Hubble data.”

NASA’s forthcoming James Webb Space Telescope will be able to follow up on the atmospheres of planets like WASP-121b with higher sensitivity than any telescope currently in space.

“This super-hot exoplanet is going to be a benchmark for our atmospheric models, and will be a great observational target moving into the Webb era,” said Hannah Wakeford, co-author and Research Fellow at the University of Exeter.

New Simulations Could Help In Hunt For Massive Mergers Of Neutron Stars, Black Holes

Now that scientists can detect the wiggly distortions in space-time created by the merger of massive black holes, they are setting their sights on the dynamics and aftermath of other cosmic duos that unify in catastrophic collisions.

Working with an international team, scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed new computer models to explore what happens when a black hole joins with a neutron star – the superdense remnant of an exploded star.

Using supercomputers to rip open neutron stars

The simulations, carried out in part at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC), are intended to help detectors home in on the gravitational-wave signals. Telescopes, too, can search for the brilliant bursts of gamma-rays and the glow of the radioactive matter that these exotic events can spew into surrounding space.

In separate papers published in a special edition of the scientific journal Classical and Quantum Gravity, Berkeley Lab and other researchers present the results of detailed simulations.

One of the studies models the first milliseconds (thousandths of a second) in the merger of a black hole and neutron star, and the other details separate simulations that model the formation of a disk of material formed within seconds of the merger, and of the evolution of matter that is ejected in the merger.

That ejected matter likely includes gold and platinum and a range of radioactive elements that are heavier than iron.

Any new information scientists can gather about how neutron stars rip apart in these mergers can help to unlock their secrets, as their inner structure and their likely role in seeding the universe with heavy elements are still shrouded in mystery.

“We are steadily adding more realistic physics to the simulations,” said – Foucart, who served as a lead author for one of the studies as a postdoctoral researcher in Berkeley Lab’s Nuclear Science Division.

“But we still don’t know what’s happening inside neutron stars. The complicated physics that we need to model make the simulations very computationally intensive.”

Finding signs of a black hole-neutron star merger

Foucart, who will soon be an assistant professor at the University of New Hampshire, added, “We are trying to move more toward actually making models of the gravitational-wave signals produced by these mergers,” which create a rippling in space-time that researchers hope can be detected with improvements in the sensitivity of experiments including Advanced LIGO, the Laser Interferometer Gravitational-Wave Observatory.

In February 2016, LIGO scientists confirmed the first detection of a gravitational wave, believed to be generated by the merger of two black holes, each with masses about 30 times larger than the Sun.

The signals of a neutron star merging with black holes or another neutron star are expected to generate gravitational waves that are slightly weaker but similar to those of black hole-black hole mergers, Foucart said.
Radioactive ‘waste’ in space

Daniel Kasen, a scientist in the Nuclear Science Division at Berkeley Lab and associate professor of physics and astronomy at UC Berkeley who participated in the research, said that inside neutron stars “there may be exotic states of matter unlike anything realized anywhere else in the universe.”

In some computer simulations the neutron stars were swallowed whole by the black hole, while in others there was a fraction of matter coughed up into space. This ejected matter is estimated to range up to about one-tenth of the mass of the Sun.

While much of the matter gets sucked into the larger black hole that forms from the merger, “the material that gets flung out eventually turns into a kind of radioactive ‘waste,'” he said. “You can see the radioactive glow of that material for a period of days or weeks, from more than a hundred million light years away.” Scientists refer to this observable radioactive glow as a “kilonova.”

The simulations use different sets of calculations to help scientists visualize how matter escapes from these mergers. By modeling the speed, trajectory, amount and type of matter, and even the color of the light it gives off, astrophysicists can learn how to track down actual events.

The weird world of neutron stars

The size range of neutron stars is set by the ultimate limit on how densely matter can be compacted, and neutron stars are among the most superdense objects we know about in the universe.

Neutron stars have been observed to have masses up to at least two times that of our sun but measure only about 12 miles in diameter, on average, while our own sun has a diameter of about 865,000 miles. At large enough masses, perhaps about three times the mass of the sun, scientists expect that neutron stars must collapse to form black holes.

A cubic inch of matter from a neutron star is estimated to weigh up to 10 billion tons. As their name suggests, neutron stars are thought to be composed largely of the neutrally charged subatomic particles called neutrons, and some models expect them to contain long strands of matter – known as “nuclear pasta” – formed by atomic nuclei that bind together.

Neutron stars are also expected to be almost perfectly spherical, with a rigid and incredibly smooth crust and an ultrapowerful magnetic field. They can spin at a rate of about 43,000 revolutions per minute (RPMs), or about five times faster than a NASCAR race car engine’s RPMs.

The aftermath of neutron star mergers

The researchers’ simulations showed that the radioactive matter that first escapes the black hole mergers may be traveling at speeds of about 20,000 to 60,000 miles per second, or up to about one-third the speed of light, as it is swung away in a long “tidal tail.”

“This would be strange material that is loaded with neutrons,” Kasen said. “As that expanding material cools and decompresses, the particles may be able to combine to build up into the heaviest elements.” This latest research shows how scientists might find these bright bundles of heavy elements.

“If we can follow up LIGO detections with telescopes and catch a radioactive glow, we may finally witness the birthplace of the heaviest elements in the universe,” he said. “That would answer one of the longest-standing questions in astrophysics.”

Most of the matter in a black hole-neutron star merger is expected to be sucked up by the black hole within a millisecond of the merger, and other matter that is not flung away in the merger is likely to form an extremely dense, thin, donut-shaped halo of matter.

The thin, hot disk of matter that is bound by the black hole is expected to form within about 10 milliseconds of the merger, and to be concentrated within about 15 to 70 miles of it, the simulations showed. This first 10 milliseconds appears to be key in the long-term evolution of these disks.

Over timescales ranging from tens of milliseconds to several seconds, the hot disk spreads out and launches more matter into space. “A number of physical processes – from magnetic fields to particle interactions and nuclear reactions – combine in complex ways to drive the evolution of the disk,” said Rodrigo Fernández, an assistant professor of physics at the University of Alberta in Canada who led one of the studies.

Simulations carried out on NERSC’s Edison supercomputer were crucial in understanding how the disk ejects matter and in providing clues for how to observe this matter, said Fernández, a former UC Berkeley postdoctoral researcher.

What’s next?

Eventually, it may be possible for astronomers scanning the night sky to find the “needle in a haystack” of radioactive kilonovae from neutron star mergers that had been missed in the LIGO data, Kasen said.

“With improved models, we are better able to tell the observers exactly which flashes of light are the signals they are looking for,” he said. Kasen is also working to build increasingly sophisticated models of neutron star mergers and supernovae through his involvement in the DOE Exascale Computing Project.

As the sensitivity of gravitational-wave detectors improves, Foucart said, it may be possible to detect a continuous signal produced by even a tiny bump on the surface of a neutron star, for example, or signals from theorized one-dimensional objects known as cosmic strings.

“This could also allow us to observe events that we have not even imagined,” he said.

Quasars May Answer How Starburst Galaxies Were Extinguished

Some of the biggest galaxies in the universe are full of extinguished stars. But nearly 12 billion years ago, soon after the universe first was created, these massive galaxies were hotspots that brewed up stars by the billions.
How these types of cosmic realms, called dusty starburst galaxies, became galactic dead zones is an enduring mystery.

Astronomers at the University of Iowa, in a new study published in the Astrophysical Journal, offer a clue. They say quasars, powerful energy sources believed to dwell at the heart of galaxies, may be responsible for why some dusty starburst galaxies ceased making stars.

The study could help explain how galaxies evolve from star makers to cosmic cemeteries and how various phenomena scientists know little about—quasars and supermassive black holes that are believed to exist deep within all galaxies, for example—may propel those changes.

The scientists arrived at their theory after locating quasars inside four dusty starburst galaxies that still are creating stars.

“These quasars may play an important role in making the dusty starbursts extinct in the cosmic history,” says Hai Fu, assistant professor in the UI’s Department of Physics and Astronomy and the paper’s first author. “This is because quasars are energetic enough to eject gas out of the galaxy, and gas is the fuel for star formation, so quasars provide a viable mechanism to explain the transition between a starburst and an extinct elliptical (galaxy).”

Quasars shouldn’t be detectable in dusty starburst galaxies because their light would be absorbed, or blocked, by the grit churned up by the intense star-forming activity taking place there, Fu says.

“So, the fact that we saw any such quasars implies that there must be more quasars hidden in dusty starbursts,” Fu says. “To push this to the extreme, maybe every dusty starburst galaxy hosts a quasar and we just cannot see the quasars.”

Fu and his team located the quasars in March 2016 with the Atacama Large Millimeter/submillimeter Array (ALMA), a bank of radio telescopes located more than 16,000 feet above sea level in northern Chile. It was the first time Fu’s team reserved time on ALMA, brought into full operation in 2013 and funded by international partners, including the U.S. National Science Foundation.

The scientists then mapped the quasars with other telescopes and at wavelengths ranging from ultraviolet to far infrared. Based on these observations, they confirmed the quasars are the same as those located with ALMA. The question then became: Why are these quasars visible when they should be enshrouded?

The researchers have a theory. They think the quasars are peeking out from deep holes in each galaxy, a debris-less vacuum that allows light to escape amid the cloudy surroundings. The specific shape of these galaxies is unclear because even ALMA isn’t powerful enough to provide a clear look at regions of the cosmos where light being detected was emitted 12 billion years ago, when the universe was roughly one-seventh its current age. But the team imagines the galaxies may be doughnut shaped and oriented in such a way that their holes (and, thus, the quasar) can be seen.

“It’s a rare case of geometry lining up,” says Jacob Isbell, a UI senior from Garrison, Iowa, majoring in physics and astronomy and the paper’s second author. “And that hole happens to be aligned with our line of sight.”
The scientists now think most quasars inside dusty starburst galaxies can’t be seen because they’re oriented in a way that keeps them hidden. But finding four examples of dusty starburst galaxies with viewable quasars does not seem random; in fact, it suggests more exist.

The paper is titled, “The circumgalactic medium of submillimeter galaxies. II. Unobscured QSOS within dusty starbursts and QSO sightlines with impact parameters below 100 kiloparsec.”

Planetary Defense Campaign Will Use Real Asteroid For The First Time

For the first time, NASA will use an actual space rock for a tabletop exercise simulating an asteroid impact in a densely populated area. The asteroid, named 2012 TC4, does not pose a threat to Earth, but NASA is using it as a test object for an observational campaign because of its close flyby on Oct. 12, 2017.

NASA has conducted such preparedness drills rehearsing various aspects of an asteroid impact, such as deflection, evacuation, and disaster relief, with other federal entities in the past. Traditionally, however, these exercises involved hypothetical impactors, prompting Vishnu Reddy of the University of Arizona’s Lunar and Planetary Laboratory to propose a slightly more realistic scenario, one that revolves around an actual near-Earth asteroid, or NEA.

“The question is, how prepared are we for the next cosmic threat?” says Reddy, an assistant professor of planetary science at the Lunar and Planetary Laboratory. “So we proposed an observational campaign to exercise the network and test how ready we are for a potential impact by a rogue asteroid.”

NASA’s Planetary Defense Coordination Office (PDCO), the federal entity in charge of coordinating efforts to protect Earth from hazardous asteroids, accepted Reddy’s proposal to conduct an observational campaign as part of assessing its Earth-based defense network. Reddy will assist Michael Kelley, who serves as a program scientist with NASA PDCO and the civil servant lead on the exercise.

The goal of the TC4 exercise is to recover, track, and characterize 2012 TC4 as a potential impactor in order to exercise the entire system from observations, modeling, prediction, and communication.

Measuring between 30 and 100 feet, roughly the same size as the asteroid that exploded over Chelyabinsk, Russia, on Feb. 15, 2013, TC4 was discovered by the Pan-STARRS 1 telescope on Oct. 5, 2012, at Haleakala Observatory on Maui, Hawaii. Given its orbital uncertainty, the asteroid will pass as close as 6,800 kilometers (4,200 miles) above Earth’s surface.

“This is a team effort that involves more than a dozen observatories, universities, and labs across the globe so we can collectively learn the strengths and limitations of our planetary defense capabilities,” said Reddy, who is coordinating the campaign for NASA PDCO.

Since its discovery in 2012, the uncertainty in the asteroid’s orbit has slowly increased, as it would for any asteroid as time passes. Therefore, the first order of business will be to “recover” the object—in other words, nail down its exact path. Reddy and his collaborators hope that depending on its predicted brightness, the asteroid would be visible again to large ground-based telescopes in late August.

“One of the strengths of UA research is partnering with federal agencies or industry to work together in solving some of the grand challenges we face,” said Kimberly Andrews Espy, senior vice president for research. “This project is a perfect example of matching UA capabilities—from our world-class imaging to our expertise in space sciences—with an external need.”

The UA is home to the Catalina Sky Survey, one of the most prolific asteroid discoverers, and the Spacewatch project that recovers and tracks faint NEAs. Both teams will take part in the planetary defense exercise.

Eclipse Balloons To Study Effect Of Mars-Like Environment On Life

Steps forward in the search for life beyond Earth can be as simple as sending a balloon into the sky. In one of the most unique and extensive eclipse observation campaigns ever attempted, NASA is collaborating with student teams across the U.S. to do just that.

A larger initiative, NASA’s Eclipse Balloon Project, led by Angela Des Jardins of Montana State University, is sending more than 50 high-altitude balloons launched by student teams across the U.S. to livestream aerial footage of the Aug. 21 total solar eclipse from the edge of space to NASA’s website.

“Total solar eclipses are rare and awe-inspiring events. Nobody has ever live-streamed aerial video footage of a total solar eclipse before,” said Angela Des Jardins. “By live-streaming it on the Internet, we are providing people across the world an opportunity to experience the eclipse in a unique way, even if they are not able to see the eclipse directly.”

A research group at NASA’s Ames Research Center, in California’s Silicon Valley, is seizing the opportunity to conduct a low-cost experiment on 34 of the balloons. This experiment, called MicroStrat, will simulate life’s ability to survive beyond Earth—and maybe even on Mars.

“The August solar eclipse gives us a rare opportunity to study the stratosphere when it’s even more Mars-like than usual,” said Jim Green, director of planetary science at NASA Headquarters in Washington. “With student teams flying balloon payloads from dozens of points along the path of totality, we’ll study effects on microorganisms that are coming along for the ride.”

NASA will provide each team with two small metal cards, each the size of a dog tag. The cards have harmless, yet environmentally resilient bacteria dried onto their surface. One card will fly up with the balloon while the other remains on the ground. A comparison of the two will show the consequences of the exposure to Mars-like conditions, such as bacterial survival and any genetic changes.

The results of the experiment will improve NASA’s understanding of environmental limits for terrestrial life, in order to inform our search for life on other worlds.

Mars’ atmosphere at the surface is about 100 times thinner than Earth’s, with cooler temperatures and more radiation. Under normal conditions, the upper portion of our stratosphere is similar to these Martian conditions, with its cold, thin atmosphere and exposure to radiation, due to its location above most of Earth’s protective ozone layer. Temperatures where the balloons fly can reach minus 35 degrees Fahrenheit (about minus 37 Celsius) or colder, with pressures about a hundredth of that at sea level.

During the eclipse, the similarities to Mars only increase. The Moon will buffer the full blast of radiation and heat from the Sun, blocking certain ultraviolet rays that are less abundant in the Martian atmosphere and bringing the temperature down even further.

“Performing a coordinated balloon microbiology experiment across the entire continental United States seems impossible under normal circumstances,” said David J. Smith of Ames, principal investigator for the experiment and mentor for the Space Life Science Training Program, the intern group developing flight hardware and logistics for this study. “The solar eclipse on August 21st is enabling unprecedented exploration through citizen scientists and students. After this experiment flies, we will have about 10 times more samples to analyze than all previously flown stratosphere microbiology missions combined.”

Student Teams Observing the Eclipse

Beyond the opportunity for NASA to conduct science, this joint project provides the opportunity for students as young as 10 years old to be exposed to the scientific method and astrobiology—research about life beyond Earth. Since ballooning is such an accessible and low-cost technique, the project has attracted student teams from Puerto Rico to Alaska.

The data collected by the teams will be analyzed by NASA scientists at Ames and NASA’s Jet Propulsion Laboratory, Pasadena, California; collaborators at Cornell University, Ithaca, New York; scientists funded by the National Science Foundation and National Oceanographic and Atmospheric Administration; faculty members and students at the teams’ institutions, as well as the public.

“This project will not only provide insight into how bacterial life responds to Mars-like conditions, we are engaging and inspiring the next generation of scientists,” said Green. “Through this exciting ‘piggyback’ mission, NASA is collaborating with scientists of the future to take a small step in the search for life beyond our planet.”

Using The Universe As A ‘Cosmological Collider’

Physicists are capitalizing on a direct connection between the largest cosmic structures and the smallest known objects to use the universe as a “cosmological collider” and investigate new physics.

The three-dimensional map of galaxies throughout the cosmos and the leftover radiation from the Big Bang – called the cosmic microwave background (CMB) – are the largest structures in the universe that astrophysicists observe using telescopes. Subatomic elementary particles, on the other hand, are the smallest known objects in the universe that particle physicists study using particle colliders.

A team including Xingang Chen of the Harvard-Smithsonian Center for Astrophysics (CfA), Yi Wang from the Hong Kong University of Science and Technology (HKUST) and Zhong-Zhi Xianyu from the Center for Mathematical Sciences and Applications at Harvard University has used these extremes of size to probe fundamental physics in an innovative way. They have shown how the properties of the elementary particles in the Standard Model of particle physics may be inferred by studying the largest cosmic structures. This connection is made through a process called cosmic inflation.

Cosmic inflation is the most widely accepted theoretical scenario to explain what preceded the Big Bang. This theory predicts that the size of the universe expanded at an extraordinary and accelerating rate in the first fleeting fraction of a second after the universe was created. It was a highly energetic event, during which all particles in the universe were created and interacted with each other. This is similar to the environment physicists try to create in ground-based colliders, with the exception that its energy can be 10 billion times larger than any colliders that humans can build.

Inflation was followed by the Big Bang, where the cosmos continued to expand for more than 13 billion years, but the expansion rate slowed down with time. Microscopic structures created in these energetic events got stretched across the universe, resulting in regions that were slightly denser or less dense than surrounding areas in the otherwise very homogeneous early universe. As the universe evolved, the denser regions attracted more and more matter due to gravity. Eventually, the initial microscopic structures seeded the large-scale structure of our universe, and determined the locations of galaxies throughout the cosmos.

In ground-based colliders, physicists and engineers build instruments to read the results of the colliding events. The question is then how we should read the results of the cosmological collider.

“Several years ago, Yi Wang and I, Nima Arkani-Hamed and Juan Maldacena from the Institute of Advanced Study, and several other groups, discovered that the results of this cosmological collider are encoded in the statistics of the initial microscopic structures. As time passes, they become imprinted in the statistics of the spatial distribution of the universe’s contents, such as galaxies and the cosmic microwave background, that we observe today,” said Xingang Chen. “By studying the properties of these statistics we can learn more about the properties of elementary particles.”

As in ground-based colliders, before scientists explore new physics, it is crucial to understand the behavior of known fundamental particles in this cosmological collider, as described by the Standard Model of particle physics.

“The relative number of fundamental particles that have different masses – what we call the mass spectrum – in the Standard Model has a special pattern, which can be viewed as the fingerprint of the Standard Model,” explained Zhong-Zhi Xiangyu. “However, this fingerprint changes as the environment changes, and would have looked very different at the time of inflation from how it looks now.”

The team showed what the mass spectrum of the Standard Model would look like for different inflation models. They also showed how this mass spectrum is imprinted in the appearance of the large-scale structure of our universe. This study paves the way for the future discovery of new physics.

“The ongoing observations of the CMB and large-scale structure have achieved impressive precision from which valuable information about the initial microscopic structures can be extracted,” said Yi Wang. “In this cosmological collider, any observational signal that deviates from that expected for particles in the Standard Model would then be a sign of new physics.”

The current research is only a small step towards an exciting era when precision cosmology will show its full power.

“If we are lucky enough to observe these imprints, we would not only be able to study particle physics and fundamental principles in the early universe, but also better understand cosmic inflation itself. In this regard, there are still a whole universe of mysteries to be explored,” said Xianyu.