Tag: Big Bang

What Happened Before the Big Bang?

A team of scientists has proposed a powerful new test for inflation, the theory that the universe dramatically expanded in size in a fleeting fraction of a second right after the Big Bang. Their goal is to give insight into a long-standing question: what was the universe like before the Big Bang?

Although cosmic inflation is well known for resolving some important mysteries about the structure and evolution of the universe, other very different theories can also explain these mysteries. In some of these theories, the state of the universe preceding the Big Bang – the so-called primordial universe – was contracting instead of expanding, and the Big Bang was thus a part of a Big Bounce.

To help decide between inflation and these other ideas, the issue of falsifiability – that is, whether a theory can be tested to potentially show it is false – has inevitably arisen. Some researchers, including Avi Loeb of the Center for Astrophysics | Harvard & Smithsonian (CfA) in Cambridge, Mass., have raised concerns about inflation, suggesting that its seemingly endless adaptability makes it all but impossible to properly test.

“Falsifiability should be a hallmark of any scientific theory. The current situation for inflation is that it’s such a flexible idea, it cannot be falsified experimentally,” Loeb said. “No matter what value people measure for some observable attribute, there are always some models of inflation that can explain it.”

Now, a team of scientists led by the CfA’s Xingang Chen, along with Loeb, and Zhong-Zhi Xianyu of the Physics Department of Harvard University, have applied an idea they call a “primordial standard clock” to the non-inflationary theories, and laid out a method that may be used to falsify inflation experimentally. The study will appear in Physical Review Letters as an Editors’ Suggestion.

In an effort to find some characteristic that can separate inflation from other theories, the team began by identifying the defining property of the various theories – the evolution of the size of the primordial universe.

“For example, during inflation, the size of the universe grows exponentially,” Xianyu said. “In some alternative theories, the size of the universe contracts. Some do it very slowly, while others do it very fast.

“The attributes people have proposed so far to measure usually have trouble distinguishing between the different theories because they are not directly related to the evolution of the size of the primordial universe,” he continued. “So, we wanted to find what the observable attributes are that can be directly linked to that defining property.”

The signals generated by the primordial standard clock can serve such a purpose. That clock is any type of heavy elementary particle in the primordial universe. Such particles should exist in any theory and their positions should oscillate at some regular frequency, much like the ticking of a clock’s pendulum.

The primordial universe was not entirely uniform. There were tiny irregularities in density on minuscule scales that became the seeds of the large-scale structure observed in today’s universe. This is the primary source of information physicists rely on to learn about what happened before the Big Bang. The ticks of the standard clock generated signals that were imprinted into the structure of those irregularities. Standard clocks in different theories of the primordial universe predict different patterns of signals, because the evolutionary histories of the universe are different.

“If we imagine all of the information we learned so far about what happened before the Big Bang is in a roll of film frames, then the standard clock tells us how these frames should be played,” Chen explained. “Without any clock information, we don’t know if the film should be played forward or backward, fast or slow, just like we are not sure if the primordial universe was inflating or contracting, and how fast it did so. This is where the problem lies. The standard clock put time stamps on each of these frames when the film was shot before the Big Bang, and tells us how to play the film.”

The team calculated how these standard clock signals should look in non-inflationary theories, and suggested how they should be searched for in astrophysical observations. “If a pattern of signals representing a contracting universe were found, it would falsify the entire inflationary theory,” Xianyu said.

The success of this idea lies with experimentation. “These signals will be very subtle to detect,” Chen said, “and so we may have to search in many different places. The cosmic microwave background radiation is one such place, and the distribution of galaxies is another. We have already started to search for these signals and there are some interesting candidates already, but we need more data.”

Many future galaxy surveys, such as US-lead LSST, European’s Euclid and the newly approved project by NASA, SphereX, are expected to provide high quality data that can be used toward the goal.

Read more at: https://phys.org/news/2019-03-big.html#jCp

The ‘Stuff’ of the Universe Keeps Changing

The composition of the universe – the elements that are the building blocks for every bit of matter – is ever-changing and ever-evolving, thanks to the lives and deaths of stars.

An outline of how those elements form as stars grow and explode and fade and merge is detailed in a review article published Jan. 31 is the journal Science.

“The universe went through some very interesting changes, where all of a sudden the periodic table – the total number of elements in the universe – changed a lot,” said Jennifer Johnson, a professor of astronomy at The Ohio State University and the article’s author.

“For 100 million years after the Big Bang, there was nothing but hydrogen, helium and lithium. And then we started to get carbon and oxygen and really important things. And now, we’re kind of in the glory days of populating the periodic table.”

The periodic table has helped humans understand the elements of the universe since the 1860s, when a Russian chemist, Dmitri Mendeleev, recognized that certain elements behaved the same way chemically, and organized them into a chart – the periodic table.

It is chemistry’s way of organizing elements, helping scientists from elementary school to the world’s best laboratories understand how materials around the universe come together.

But, as scientists have long known, the periodic table is just made of stardust: Most elements on the periodic table, from the lightest hydrogen to heavier elements like lawrencium, started in stars.
The table has grown as new elements have been discovered – or in cases of synthetic elements, have been created in laboratories around the world – but the basics of Mendeleev’s understanding of atomic weight and the building blocks of the universe have held true.

Nucleosynthesis – the process of creating a new element – began with the Big Bang, about 13.7 billion years ago. The lightest elements in the universe, hydrogen and helium, were also the first, results of the Big Bang. But heavier elements – just about every other element on the periodic table – are largely the products of the lives and deaths of stars.

Johnson said that high-mass stars, including some in the constellation Orion, about 1,300 light years from Earth, fuse elements much faster than low-mass stars. These grandiose stars fuse hydrogen and helium into carbon, and turn carbon into magnesium, sodium and neon. High-mass stars die by exploding into supernovae, releasing elements – from oxygen to silicon to selenium – into space around them.

Smaller, low-mass stars – stars about the size of our own Sun – fuse hydrogen and helium together in their cores. That helium then fuses into carbon. When the small star dies, it leaves behind a white dwarf star. White dwarfs synthesize other elements when they merge and explode. An exploding white dwarf might send calcium or iron into the abyss surrounding it. Merging neutron stars might create rhodium or xenon. And because, like humans, stars live and die on different time scales – and because different elements are produced as a star goes through its life and death – the composition of elements in the universe also changes over time.

“One of the things I like most about this is how it takes several different processes for stars to make elements and these processes are interestingly distributed across the periodic table,” Johnson said. “When we think of all the elements in the universe, it is interesting to think about how many stars gave their lives – and not just high-mass stars blowing up into supernovae. It’s also some stars like our Sun, and older stars. It takes a nice little range of stars to give us elements.”

Hubble Finds Clues to the Birth of Supermassive Black Holes

Astrophysicists have taken a major step forward in understanding how supermassive black holes formed. Using data from Hubble and two other space telescopes, Italian researchers have found the best evidence yet for the seeds that ultimately grow into these cosmic giants.

supermassive-black-hole-seed

For years astronomers have debated how the earliest generation of supermassive black holes formed very quickly, relatively speaking, after the Big Bang. Now, an Italian team has identified two objects in the early Universe that seem to be the origin of these early supermassive black holes. The two objects represent the most promising black hole seed candidates found so far.

The group used computer models and applied a new analysis method to data from the NASA Chandra X-ray Observatory, the NASA/ESA Hubble Space Telescope, and the NASA Spitzer Space Telescope to find and identify the two objects. Both of these newly discovered black hole seed candidates are seen less than a billion years after the Big Bang and have an initial mass of about 100 000 times the Sun.

“Our discovery, if confirmed, would explain how these monster black holes were born,” said Fabio Pacucci, lead author of the study, of Scuola Normale Superiore in Pisa, Italy.

This new result helps to explain why we see supermassive black holes less than one billion years after the Big Bang.

There are two main theories to explain the formation of supermassive black holes in the early Universe. One assumes that the seeds grow out of black holes with a mass about ten to a hundred times greater than our Sun, as expected for the collapse of a massive star. The black hole seeds then grew through mergers with other small black holes and by pulling in gas from their surroundings. However, they would have to grow at an unusually high rate to reach the mass of supermassive black holes already discovered in the billion years young Universe.

The new findings support another scenario where at least some very massive black hole seeds with 100 000 times the mass of the Sun formed directly when a massive cloud of gas collapses. In this case the growth of the black holes would be jump started, and would proceed more quickly.

“There is a lot of controversy over which path these black holes take,” said co-author Andrea Ferrara also of Scuola Normale Superiore. “Our work suggests we are converging on one answer, where black holes start big and grow at the normal rate, rather than starting small and growing at a very fast rate.”

Andrea Grazian, a co-author from the National Institute for Astrophysics in Italy explains: “Black hole seeds are extremely hard to find and confirming their detection is very difficult. However, we think our research has uncovered the two best candidates so far.”

Even though both black hole seed candidates match the theoretical predictions, further observations are needed to confirm their true nature. To fully distinguish between the two formation theories, it will also be necessary to find more candidates.

The team plans to conduct follow-up observations in X-rays and in the infrared range to check whether the two objects have more of the properties expected for black hole seeds. Upcoming observatories, like the NASA/ESA/CSA James Webb Space Telescope and the European Extremely Large Telescope will certainly mark a breakthrough in this field, by detecting even smaller and more distant black holes.