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Astronomers Have Found the Universe’s Missing Matter

Astronomers Have Found the Universe's Missing Matter 86

Astronomers have finally found the last of the missing universe. It’s been hiding since the mid-1990s, when researchers decided to inventory all the “ordinary” matter in the cosmos—stars and planets and gas, anything made out of atomic parts. (This isn’t “dark matter,” which remains a wholly separate enigma.) They had a pretty good idea of how much should be out there, based on theoretical studies of how matter was created during the Big Bang. Studies of the cosmic microwave background (CMB)—the leftover light from the Big Bang—would confirm these initial estimates.

So they added up all the matter they could see—stars and gas clouds and the like, all the so-called baryons. They were able to account for only about 10 percent of what there should be. And when they considered that ordinary matter makes up only 15 percent of all matter in the universe—dark matter makes up the rest—they had only inventoried a mere 1.5 percent of all matter in the universe.

Now, in a series of three recent papers, astronomers have identified the final chunks of all the ordinary matter in the universe. (They are still deeply perplexed as to what makes up dark matter.) And despite the fact that it took so long to identify it all, researchers spotted it right where they had expected it to be all along: in extensive tendrils of hot gas that span the otherwise empty chasms between galaxies, more properly known as the warm-hot intergalactic medium, or WHIM.

Early indications that there might be extensive spans of effectively invisible gas between galaxies came from computer simulations done in 1998. “We wanted to see what was happening to all the gas in the universe,” said Jeremiah Ostriker, a cosmologist at Princeton University who constructed one of those simulations along with his colleague Renyue Cen. The two ran simulations of gas movements in the universe acted on by gravity, light, supernova explosions and all the forces that move matter in space. “We concluded that the gas will accumulate in filaments that should be detectable,” he said.

Except they weren’t — not yet.

“It was clear from the early days of cosmological simulations that many of the baryons would be in a hot, diffuse form — not in galaxies,” said Ian McCarthy, an astrophysicist at Liverpool John Moores University. Astronomers expected these hot baryons to conform to a cosmic superstructure, one made of invisible dark matter, that spanned the immense voids between galaxies. The gravitational force of the dark matter would pull gas toward it and heat the gas up to millions of degrees. Unfortunately, hot, diffuse gas is extremely difficult to find.

To spot the hidden filaments, two independent teams of researchers searched for precise distortions in the CMB, the afterglow of the Big Bang. As that light from the early universe streams across the cosmos, it can be affected by the regions that it’s passing through. In particular, the electrons in hot, ionized gas (such as the WHIM) should interact with photons from the CMB in a way that imparts some additional energy to those photons. The CMB’s spectrum should get distorted.

Unfortunately the best maps of the CMB (provided by the Planck satellite) showed no such distortions. Either the gas wasn’t there, or the effect was too subtle to show up.

But the two teams of researchers were determined to make them visible. From increasingly detailed computer simulations of the universe, they knew that gas should stretch between massive galaxies like cobwebs across a windowsill. Planck wasn’t able to see the gas between any single pair of galaxies. So the researchers figured out a way to multiply the faint signal by a million.

First, the scientists looked through catalogs of known galaxies to find appropriate galaxy pairs — galaxies that were sufficiently massive, and that were at the right distance apart, to produce a relatively thick cobweb of gas between them. Then the astrophysicists went back to the Planck data, identified where each pair of galaxies was located, and then essentially cut out that region of the sky using digital scissors. With over a million clippings in hand (in the case of the study led by Anna de Graaff, a Ph.D. student at the University of Edinburgh), they rotated each one and zoomed it in or out so that all the pairs of galaxies appeared to be in the same position. They then stacked a million galaxy pairs on top of one another. (A group led by Hideki Tanimura at the Institute of Space Astrophysics in Orsay, France, combined 260,000 pairs of galaxies.) At last, the individual threads — ghostly filaments of diffuse hot gas — suddenly became visible.

(A) Images of one million galaxy pairs were aligned and added together.
(B) Astronomers mapped all the gas within the actual galaxies.
(C) By subtracting the galaxies (B) from the initial image (A), researchers revealed filamentary gas hiding in intergalactic space.Adapted by Quanta Magazine

The technique has its pitfalls. The interpretation of the results, said Michael Shull, an astronomer at the University of Colorado at Boulder, requires assumptions about the temperature and spatial distribution of the hot gas. And because of the stacking of signals, “one always worries about ‘weak signals’ that are the result of combining large numbers of data,” he said. “As is sometimes found in opinion polls, one can get erroneous results when one has outliers or biases in the distribution that skew the statistics.”

In part because of these concerns, the cosmological community didn’t consider the case settled. What was needed was an independent way of measuring the hot gas. This summer, one arrived.

Lighthouse Effect

While the first two teams of researchers were stacking signals together, a third team followed a different approach. They observed a distant quasar — a bright beacon from billions of light-years away — and used it to detect gas in the seemingly empty intergalactic spaces through which the light traveled. It was like examining the beam of a faraway lighthouse in order to study the fog around it.

Usually when astronomers do this, they try to look for light that has been absorbed by atomic hydrogen, since it is the most abundant element in the universe. Unfortunately, this option was out. The WHIM is so hot that it ionizes hydrogen, stripping its single electron away. The result is a plasma of free protons and electrons that don’t absorb any light.

Fabrizio Nicastro used light from a quasar to track the missing gas.Courtesy of Fabrizio Nicastro

So the group decided to look for another element instead: oxygen. While there’s not nearly as much oxygen as hydrogen in the WHIM, atomic oxygen has eight electrons, as opposed to hydrogen’s one. The heat from the WHIM strips most of those electrons away, but not all. The team, led by Fabrizio Nicastro of the National Institute for Astrophysics in Rome, tracked the light that was absorbed by oxygen that had lost all but two of its electrons. They found two pockets of hot intergalactic gas. The oxygen “provides a tracer of the much larger reservoir of hydrogen and helium gas,” said Shull, who is a member of Nicastro’s team. The researchers then extrapolated the amount of gas they found between Earth and this particular quasar to the universe as a whole. The result suggested that they had located the missing 30 percent.

The number also agrees nicely with the findings from the CMB studies. “The groups are looking at different pieces of the same puzzle and are coming up with the same answer, which is reassuring, given the differences in their methods,” said Mike Boylan-Kolchin, an astronomer at the University of Texas, Austin.

The next step, said Shull, is to observe more quasars with next-generation X-ray and ultraviolet telescopes with greater sensitivity. “The quasar we observed was the best and brightest lighthouse that we could find. Other ones will be fainter, and the observations will take longer,” he said. But for now, the takeaway is clear. “We conclude that the missing baryons have been found,” their team wrote.

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Space

KOI-5Ab, the curious planet that orbits in a system of three suns

KOI-5Ab, the curious planet that orbits in a system of three suns 99
Photo: (Caltech / R. Hurt (IPAC))

To us, the Sun alone seems perfectly normal, but our solar system is actually a strange exception.

Most stars in the Milky Way galaxy have at least one companion star. In a system 1,800 light-years away, astronomers have finally confirmed the existence of a gas giant planet orbiting stars in a triple star system.

Called KOI-5, the system is located in the constellation Cygnus, and the exoplanet was confirmed ten years after it was first detected by the Kepler space telescope.

In fact, the planet – now known as KOI-5Ab – was discovered by Kepler when it began operations back in 2009.

“KOI-5Ab was dropped because it was difficult and we had thousands of other candidates,” astronomer David Siardi of NASA’s Exoplanet Science Institute said.

“There were lighter dives than the KOI-5Ab, and every day we learned something new from Kepler, so the KOI-5 was almost forgotten.”

Exoplanet hunters tend to avoid the complexities of multi-star systems; of the more than 4,300 exoplanets confirmed to date, less than 10 percent are multi-star systems, although such systems dominate the galaxy. As a result, little is known about the properties of exoplanets in multi-star systems compared to those orbiting a lone star.

After Kepler’s discovery, Chardy and other astronomers used ground-based telescopes such as the Palomar Observatory, Keck Observatory, and the Gemini North Telescope to study the system. By 2014, they had identified two companion stars, KOI-5B and KOI-5C.

Scientists were able to establish that the planet KOI-5Ab, is a gas giant that is about half the mass of Saturn and 7 times the size of Earth, and is in a very close five-day orbit around KOI-5A. KOI-5A and KOI-5B, both of roughly the same mass as the Sun, form a relatively close binary system with an orbital period of about 30 years.

KOI-5Ab, the curious planet that orbits in a system of three suns 100

A third star, KOI-5C, orbits the binary system at a much greater distance, with a period of about 400 years – slightly longer than Pluto’s 248-year orbit.

“By studying this system in more detail, perhaps we can understand how planets are created in the universe.”

The discovery was announced at the 237th meeting of the American Astronomical Society.

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Space

Why the universe does not fit into science

Why the universe does not fit into science 101
Photo: YouTube

Science can be compared to an artist painting what he has never seen, or to a writer describing other people’s travels: objects that he has never seen, places where he has never been. Sometimes such scientific “arts” turn out to be beautiful and interesting, but most of them will forever remain only theories, because they are beyond human capabilities.

In fact, science has the right only to speculate: how our universe appeared, how old it is, how many stars and other objects it contains.

Universe model

Why the universe does not fit into science 102

How many stars are there in the sky?

With an unarmed eye, a person can see about nine thousand stars in the sky in one cloudless and moonless night. And armed with binoculars or a telescope, much more – up to several million. However, this is much less than their true number in the universe. Indeed, only in our one galaxy (the Milky Way) there are about 400 billion stars. The exact amount, of course, is not known to science. And the visible universe contains about 170 billion galaxies.

It is worth clarifying that scientists can see the universe 46 billion light years deep in all directions. And the visible (observable) universe includes the space accessible to our eyes from the moment of the Big Explosion. In other words, only this (accessible to human perception) space science refers to our universe. Science does not consider everything that follows.

It is believed that there are supposedly a ceptillion (10 to 24 degrees) stars in our universe. These are theoretical calculations based on the approximate size and age of the universe. The origin of the universe is explained by the Big Bang theory. This is why the universe is constantly expanding and the more time passes, the more complex the universe and its components become.

Why the universe does not fit into science 103

It is not entirely correct to consider and perceive this scientific theory “head-on”. Scientists always claim that that explosion was not exactly an explosion, and the point that exploded was not the only one. After all, it was everywhere, because space did not exist then. And in general – everything happened quite differently from what is described in the Big Bang theory, but all other descriptions of the origin of the universe are even more incredible and inaccurate.

Separate but interconnected

That which is beyond the reach of human perception is usually discarded by science, or recognized as non-existent. Recognizing one thing, science does not want to recognize the existence of the other, although everything in our world is interconnected and is not able to exist separately – by itself.

Each object of the universe is a part of it much more than an independent, separate object.

Any person, like any material object of our world, consists of components: organs, cells, molecules, atoms. And each of its constituent parts can represent the whole world. Separate, and at the same time connected with all the others.

However, science, as a rule, perceives all the components of the universe – people, animals, plants, objects, the Earth, the Sun, other planets and stars – as separate subjects, thereby limiting itself.

Why the universe does not fit into science 104

Even what is considered the visible universe, one of the atoms of which could be called our solar system, is not subject to the boundaries of human perception. But perhaps the atom is an exaggeration, and our solar system is not even an atom, but one of its elements!

How, being so far from the truth, can one reason about something with the degree of probability with which science tries to reason about the origin of the universe?

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Space

An unexplained wobble shifts the poles of Mars

An unexplained wobble shifts the poles of Mars 105

The red planet sways from side to side like a whirligig when it loses speed. The new study allowed scientists to notice that the poles of Mars deviate slightly from the axis of rotation of the planet. On average, they move 10 cm from the center with a period of 200 days.

Such changes are called the Chandler Oscillations  – after the American astronomer Seth Chandler, who discovered them in 1891. Previously, they were only seen on Earth. It is known that the displacement of the poles of rotation of our planet occurs with a period of 433 days, while the amplitude reaches 15 meters. There is no exact answer why this is happening. It is believed that the fluctuations are influenced by processes in the ocean and the Earth’s atmosphere.

Chandler’s wobbles on Mars are equally perplexing. The authors of the study discovered them by comparing data from 18 years of studying the planet. The information was obtained thanks to three spacecraft that orbit the Red Planet: Mars Odyssey, Mars Reconnaissance Orbiter and Mars Global Surveyor. 

Since Mars has no oceans, it is likely that the Red Planet’s wobbly rotation is due to changes in atmospheric pressure. This is the first explanation that researchers have shared. In the future, there should be new details about the fluctuations that have so interested the scientific community.

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