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Important threshold exceeded in the mystery of the rate of expansion of the universe



  The mystery of the expansion rate of the universe is being extended

This is a ground-based telescope that looks at the Great Magellanic Cloud, a satellite galaxy of our Milky Way, from a distance. The image taken by the Hubble Space Telescope shows one of the many star clusters scattered throughout the dwarf galaxy. The cluster members include a special class of pulsating stars, a cepheid variable that lightens and dims at a predictable speed that matches their intrinsic brightness. Once astronomers have determined this value, they can measure the light of these stars to calculate an exact distance to the galaxy. If the new Hubble observations are correlated with an independent distance measurement technique to the Large Magellanic Cloud (with simple trigonometry), the researchers were able to strengthen the basis of the so-called "cosmic distance ladder". This "fine-tuning" has this "fine-tuning." The accuracy of the rate at which the universe expands was called the Hubble constant. Credits: NASA, ESA, A. Riess (STScI / JHU), and Palomar Digitalized Sky Survey

Astronomers using NASA's Hubble Space Telescope say they have crossed an important threshold to a discrepancy between the two most important ones Demonstrate techniques for measuring the rate of expansion 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 suggest a faster rate of expansion in the modern universe than expected, depending on how the universe appeared 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, however, it was unclear whether differences in measurement techniques are responsible or whether the difference could be due to unfortunate measurements. Discrepancy is only 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 may be needed to explain the mismatch. [19659004] "The tension between the early and the late Universe is 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 you really can not dismiss as coincidence. This inequality could not seem plausible by accident. "

Tightening the screws on the" cosmic spacer ladder "

Scientists use a" cosmic distance ladder "to determine how far away 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 it traverses an expanding universe to calculate how fast the cosm expands over time, a value known as the Hubble constant. Riess and his SH0ES team (Supernovae H0 for the Equation of State) have been seeking refinement of Hubble distance measurements and Hubble constant fine tuning since 2005.

In this new study, astronomers Hubble used to observe pulsing stars called the Cepheid Variables in the Large Magellanic Cloud at 70. 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 have become more precise, their calculation of the Hubble constant has been in conflict 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 several times.

"These are not just two experiments that do not match," explained Riess. "We measure something fundamentally different. One is a measure of 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 ​​do not match, there is a very high probability that something is missing in the cosmological model that connects the two epochs.

  The Universe Expansion Rate Grows with New Hubble Data

This illustration shows the three basic steps that astronomers use to calculate how fast the universe expands over time, a value called the Hubble constant becomes. All steps involve building a strong "cosmic distance ladder" by first measuring exact distances to nearby galaxies and then moving them to more distant galaxies. These "ladders" are a series of measurements of different types of astronomical objects with an intrinsic brightness that researchers can use to calculate distances. The most reliable for shorter distances are Cepheid variables, stars that pulsate at predictable rates that indicate their intrinsic brightness. Astronomers recently used the Hubble Space Telescope to observe 70 Cepheid variables in the nearby Large Magellanic Cloud to provide the most accurate distance measurement to that galaxy. Astronomers compare the measurements of nearby Cepheids with those in more distant galaxies, which include another cosmic scale, namely, exploding stars called the Type Ia supernova. These supernovas are much brighter than Cepheid variables. Astronomers use them as milestones to measure the distance from Earth to distant galaxies. Each of these markers builds on the previous step in the ladder. By extending the ladder with different types of reliable Milepost markers, astronomers can reach very large distances in the universe. Astronomers compare these distance values ​​with measurements of the light of an entire galaxy, which become increasingly redder due to the uniform expansion of space with increasing distance. Astronomers can then calculate how fast the cosm expands: the Hubble constant. Credits: NASA, ESA, and A. Feild (STScI)

How the new study was conducted

Astronomers use Cepheid variables as cosmic yardsticks to near intergalactic distances for over a century measure up. 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 used Hubble 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 guide stars, he can only observe one cepheid per 90-minute Hubble orbit around the Earth. Therefore, it would be very expensive for the telescope to observe every cepheid, "said team member Stefano Casertano, also from STScI and Johns Hopkins. "Instead, we searched for groups of Cepheids that were close enough that we could move between them without recalibrating the telescope. These Cepheids are so bright that we only have to watch them for two seconds. This technique allows us to observe a dozen Cepheids for the duration of an orbit. So we stay in control of the gyroscope and do the DASHing very fast.

Hubble astronomers then combined their findings with other observations from the Araucaria Project, a collaboration between astronomers from facilities 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 extends deeper into space.

The new estimate of the Hubble constant is 74 kilometers per second and second. 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 taken from the Planck observations of the early universe, paired with our current understanding of the universe. [19659004 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 space and started the initial expansion. Dark energy could also be the reason for today's accelerated expansion of the universe. 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 constants, 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, which are produced in nuclear reactions and radioactive decays.

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 team's results 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.


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