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HubbleSite: News – The new expansion rates of the universe are enhanced by new Hubble data



  Mystery of the Universe's Expansion Rate with New Hubble Data

Astronomers using NASA's Hubble Space Telescope say they have crossed an important threshold to discrepancy between the two most important techniques for measuring expansion rate of the universe. The recent study confirms that new theories may be needed to explain the forces that shaped the cosmos.

A quick summary: The universe is getting bigger by the second. The space between the galaxies expands like the dough that rises in the oven. But how fast does the universe expand? As Hubble and other telescopes try to answer that question, they come across a fascinating difference between what scientists predict and what they observe.

Hubble measurements indicate a faster rate of expansion in the modern universe than expected, based on the appearance of the universe more than 1

3 billion years ago. These measurements of the early universe come from the Planck satellite of the European Space Agency. This discrepancy has been noted in recent years in scientific papers, but it was unclear whether differences in measurement techniques are responsible or whether the difference could be due to unfortunate measurements.

The latest Hubble data reduces the likelihood that this will be the case Discrepancy is just a coincidence to 1: 100,000. This is a significant gain from a previous estimate of less than a year ago from a 1: 3,000 chance.

These most accurate Hubble measurements support the notion that new physics might be needed to explain the mismatch.

"The Hubble tension between the early and late Universe may be the most exciting development in cosmology in decades," said senior researcher and Nobel laureate Adam Riess of the Space Telescope Science Institute (STScI) and Johns Hopkins University in Baltimore , Maryland. "This mismatch has grown and has now reached a point that really can not be dismissed as coincidence, and this inequality could not be plausible by accident."

Tightening the Screws on the "Cosmic Spacer"

Scientists use a "cosmic ladder" to determine how far things are in the universe. This method depends on accurate distance measurements to nearby galaxies and then moves to more distant galaxies, using their stars as mile marker markers. Astronomers use these values ​​along with other measurements of galaxy light that redden as you cross an expanding universe to calculate how fast the cosm expands over time. This value is called the Hubble constant. Riess and his team SH0ES (Supernovae H 0 for the State of State of State) are since 2005 looking for distance measurements with Hubble and the fine tuning of the Hubble constant.

In this new study astronomers Hubble used to observe 70 pulsating stars, so-called Cepheid variables, in the Large Magellanic Cloud. The observations helped astronomers "rebuild" the distance ladder by improving the comparison between these Cepheids and their more distant cousins ​​in the galactic supernova hosts. Riess' team reduced the uncertainty in their Hubble constant value from 2.2% formerly to 1.9%.

As the team's measurements became more precise, their calculation of the Hubble constant remained inconsistent with the expected value of the expansion of the early Universe derived from observations. These measurements were taken by Planck, who is mapping the cosmic microwave background, an afterglow of 380,000 years after the Big Bang.

The measurements have been thoroughly reviewed so that astronomers can not currently dismiss the gap between the two results as due to a problem error in a single measurement or method. Both values ​​were tested in different ways.

"These are not just two experiments that do not match," explained Riess. "We measure something fundamentally different: on the one hand, we measure how fast the universe expands from today's perspective, the other is a prediction based on the physics of the early Universe and measurements of how fast it should expand if these values ​​are not There is a very high probability that something is missing in the cosmological model that connects the two epochs. "

How the New Study Was Performed

Astronomers use Cepheid variables as cosmic yardsticks to match to measure near intergalactic distances for over a century. However, trying to harvest a bunch of these stars was so time-consuming that it was almost unattainable. The team used a clever new method called DASH (Drift And Shift), which Hubble used as a point-and-shoot camera to capture fast images of extremely bright, pulsating stars, eliminating the time-consuming need for accurate shots Demonstrate.

"When Hubble uses precise pointing by focusing on beacons, he can only observe one cepheid per 90-minute Hubble orbit around the earth, so it would be very expensive if the telescope could observe any cepheid," explained he Stefano Casertano, also a member of STScI and Johns Hopkins. "Instead, we searched for clusters of Cepheids that were so close together that we could move between them without re-calibrating the telescope's alignment.These Cepheids are so bright we only need to watch them for a couple of dozen Cepheids for the duration of an orbit, so we stay in control of the gyroscope and perform DASHing very quickly. "

Hubble astronomers then combined their findings with other observations from the Araucaria Project, a collaboration between astronomers from institutions in Chile. the US and Europe. This group performed range measurements on the Large Magellanic Cloud by observing the dimming of light as a star passes in front of its partner in the darkening of binary star systems.

The combined measurements helped the SH0ES team refine the true brightness of the Cepheids. With this more accurate result, the team could then "tighten" the screws of the remaining ladder that reaches deeper into space.

The new estimate of the Hubble constant is 74 kilometers per second per megaparsek. This means that every 3.3 million light-years further away is a galaxy away from us. It seems to be moving 74 kilometers per second faster due to the expansion of the universe. The number indicates that the universe expands 9% faster than the prediction of 67 kilometers per second per megaparsec, which derives from Planck's observations of the early universe, coupled with our present-day understanding of the universe. [19659003] What could explain this discrepancy?

One explanation for the mismatch is the unexpected appearance of dark energy in the young universe, which is now thought to make up 70% of the universe's content. The theories proposed by John Hopkins astronomers are referred to as "early dark energy" and suggest that the universe has evolved as a three-act game.

Astronomers have already hypothesized that dark energy exists in the first few seconds after the Big Bang and matter has pushed through the room and started the initial expansion. The dark energy may also be the reason for the accelerated expansion of the universe today. The new theory suggests that not long after the Big Bang there was a third episode of dark energy that extended the universe faster than astronomers had predicted. The existence of this "early dark energy" could be responsible for the voltage between the two Hubble constant values, said Riess.

Another idea is that the universe contains a new subatomic particle that moves near the speed of light. Such fast particles are collectively referred to as "dark radiation" and include already known particles, such as neutrinos, resulting from nuclear reactions and radioactive decomposition.

Another attractive possibility is that dark matter (an invisible form of matter that does not consist of protons) (neutrons and electrons) interacts more with normal matter or radiation than previously thought.

The true explanation, however, is still a mystery.

Riess has no answer to this annoying problem, but his team will continue using Hubble to reduce the uncertainties in the Hubble constant. Their goal is to reduce the uncertainty to 1%, which should help astronomers determine the cause of the discrepancy.

The results of the team were accepted for publication in the Astrophysical Journal.

The Hubble Space Telescope is an international collaboration project between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, is conducting Hubble science operations. STScI is being named for NASA by the Association of Universities for Astronomy Research of Washington, D.C. operated.


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