H0LiCOW! Cosmic Magnifying Glasses Yield Independent Measure of Universe’s Expansion That Adds to Troubling Discrepancy – SciTechDaily

Each of these Hubble Space Telescope snapshots reveals four distorted images of a background quasar surrounding the central core of a foreground massive galaxy.The multiple quasar images were produced by the gravity of the foreground galaxy, which is acting like a magnifying glass by warping the quasars light in an effect called gravitational lensing. Quasars are extremely distant cosmic streetlights produced by active black holes.The light rays from each lensed quasar image take a slightly different path through space to reach Earth. The pathways length depends on the amount of matter that is distorting space along the line of sight to the quasar. To trace each pathway, the astronomers monitor the flickering of the quasars light as its black hole gobbles up material. When the light flickers, each lensed image brightens at a different time. This flickering sequence allows researchers to measure the time delays between each image as the lensed light travels along its path to Earth.These time-delay measurements helped astronomers calculate how fast the universe is growing, a value called the Hubble constant.The Hubble images were taken between 2003 and 2004 with the Advanced Camera for Surveys.Credit: NASA, ESA, S.H. Suyu (Max Planck Institute for Astrophysics, Technical University of Munich, and Academia Sinica Institute of Astronomy and Astrophysics), and K.C. Wong (University of Tokyos Kavli Institute for the Physics and Mathematics of the Universe)

People use the phrase Holy Cow to express excitement. Playing with that phrase, researchers from an international collaboration developed an acronymH0LiCOWfor their projects name that expresses the excitement over their Hubble Space Telescope measurements of the universes expansion rate.

Knowing the precise value for how fast the universe expands is important for determining the age, size, and fate of the cosmos. Unraveling this mystery has been one of the greatest challenges in astrophysics in recent years.

Members of the H0LiCOW (H0 Lenses in COSMOGRAILs Wellspring) team used Hubble and a technique that is completely independent of any previous method to measure the universes expansion, a value called the Hubble constant.

This latest value represents the most precise measurement yet using the gravitational lensing method, where the gravity of a foreground galaxy acts like a giant magnifying lens, amplifying and distorting light from background objects. This latest study did not rely on the traditional cosmic distance ladder technique to measure accurate distances to galaxies by using various types of stars as milepost markers. Instead, the researchers employed the exotic physics of gravitational lensing to calculate the universes expansion rate.

The researchers result further strengthens a troubling discrepancy between the expansion rate calculated from measurements of the local universe and the rate as predicted from background radiation in the early universe, a time before galaxies and stars even existed. The new study adds evidence to the idea that new theories may be needed to explain what scientists are finding.

This graphic lists the variety of techniques astronomers have used to measure the expansion rate of the universe, known as the Hubble constant. Knowing the precise value for how fast the universe expands is important for determining the age, size, and fate of the cosmos.One set of observations looked at the very early universe. Based on those measurements, astronomers calculated a Hubble constant value. A second set of observation strategies analyzed the universes expansion in the local universe.The challenge to cosmologists is that these two approaches dont arrive at the same value. Its just as perplexing as two opposite sections of a bridge under construction not lining up. Clearly something is wrong, but what? Astrophysicists may need to rethink their ideas about the physical underpinnings of the observable universe.The top half of the illustration outlines the seven different methods used to measure the expansion in the local universe. The letters corresponding to each technique are plotted on the bridge on the right. The location of each dot on the bridge road represents the measured value of the Hubble constant, while the length of the associated bar shows the estimated amount of uncertainty in the measurements. The seven methods combined yield an average Hubble constant value of 73 kilometers per second per megaparsec.This number is at odds with the combined value of the techniques astronomers used to calculate the universes expansion rate from the early cosmos (shown in the bottom half of the graphic). However, these five techniques are generally more precise because they have lower estimated uncertainties, as shown in the plot on the bridge road. Their combined value for the Hubble constant is 67.4 kilometers per second per megaparsec.Credit: NASA, ESA, and A. James (STScI)

A team of astronomers using NASAs Hubble Space Telescope has measured the universes expansion rate using a technique that is completely independent of any previous method.

Knowing the precise value for how fast the universe expands is important for determining the age, size, and fate of the cosmos. Unraveling this mystery has been one of the greatest challenges in astrophysics in recent years. The new study adds evidence to the idea that new theories may be needed to explain what scientists are finding.

The researchers result further strengthens a troubling discrepancy between the expansion rate, called the Hubble constant, calculated from measurements of the local universe and the rate as predicted from background radiation in the early universe, a time before galaxies and stars even existed.

This latest value represents the most precise measurement yet using the gravitational lensing method, where the gravity of a foreground galaxy acts like a giant magnifying lens, amplifying and distorting light from background objects. This latest study did not rely on the traditional cosmic distance ladder technique to measure accurate distances to galaxies by using various types of stars as milepost markers. Instead, the researchers employed the exotic physics of gravitational lensing to calculate the universes expansion rate.

Annotated Compass Image of Gravitationally Lensed Quasars. Credit: NASA, ESA, S.H. Suyu (Max Planck Institute for Astrophysics, Technical University of Munich, and Academia Sinica Institute of Astronomy and Astrophysics), and K.C. Wong (University of Tokyos Kavli Institute for the Physics and Mathematics of the Universe)

The astronomy team that made the new Hubble constant measurements is dubbed H0LiCOW (H0 Lenses in COSMOGRAILs Wellspring). COSMOGRAIL is the acronym for Cosmological Monitoring of Gravitational Lenses, a large international project whose goal is monitoring gravitational lenses. Wellspring refers to the abundant supply of quasar lensing systems.

The research team derived the H0LiCOW value for the Hubble constant through observing and analysis techniques that have been greatly refined over the past two decades.

H0LiCOW and other recent measurements suggest a faster expansion rate in the local universe than was expected based on observations by the European Space Agencys Planck satellite of how the cosmos behaved more than 13 billion years ago.

The gulf between the two values has important implications for understanding the universes underlying physical parameters and may require new physics to account for the mismatch.

If these results do not agree, it may be a hint that we do not yet fully understand how matter and energy evolved over time, particularly at early times, said H0LiCOW team leader Sherry Suyu of the Max Planck Institute for Astrophysics in Germany, the Technical University of Munich, and the Academia Sinica Institute of Astronomy and Astrophysics in Taipei, Taiwan.

The H0LiCOW team used Hubble to observe the light from six faraway quasars, the brilliant searchlights from gas orbiting supermassive black holes at the centers of galaxies. Quasars are ideal background objects for many reasons; for example, they are bright, extremely distant, and scattered all over the sky. The telescope observed how the light from each quasar was multiplied into four images by the gravity of a massive foreground galaxy. The galaxies studied are 3 billion to 6.5 billion light-years away. The quasars average distance is 5.5 billion light-years from Earth.

The light rays from each lensed quasar image take a slightly different path through space to reach Earth. The pathways length depends on the amount of matter that is distorting space along the line of sight to the quasar. To trace each pathway, the astronomers monitor the flickering of the quasars light as its black hole gobbles up material. When the light flickers, each lensed image brightens at a different time.

This flickering sequence allows researchers to measure the time delays between each image as the lensed light travels along its path to Earth. To fully understand these delays, the team first used Hubble to make accurate maps of the distribution of matter in each lensing galaxy. Astronomers could then reliably deduce the distances from the galaxy to the quasar, and from Earth to the galaxy and to the background quasar. By comparing these distance values, the researchers measured the universes expansion rate.

The length of each time delay indicates how fast the universe is expanding, said team member Kenneth Wong of the University of Tokyos Kavli Institute for the Physics and Mathematics of the Universe, lead author of the H0LiCOW collaborations most recent paper. If the time delays are shorter, then the universe is expanding at a faster rate. If they are longer, then the expansion rate is slower.

The time-delay process is analogous to four trains leaving the same station at exactly the same time and traveling at the same speed to reach the same destination. However, each of the trains arrives at the destination at a different time. Thats because each train takes a different route, and the distance for each route is not the same. Some trains travel over hills. Others go through valleys, and still others chug around mountains. From the varied arrival times, one can infer that each train traveled a different distance to reach the same stop. Similarly, the quasar flickering pattern does not appear at the same time because some of the light is delayed by traveling around bends created by the gravity of dense matter in the intervening galaxy.

The researchers calculated a Hubble constant value of 73 kilometers per second per megaparsec (with 2.4% uncertainty). This means that for every additional 3.3 million light-years away a galaxy is from Earth, it appears to be moving 73 kilometers per second faster, because of the universes expansion.

The teams measurement also is close to the Hubble constant value of 74 calculated by the Supernova H0 for the Equation of State (SH0ES) team, which used the cosmic distance ladder technique. The SH0ES measurement is based on gauging the distances to galaxies near and far from Earth by using Cepheid variable stars and supernovas as measuring sticks to the galaxies.

The SH0ES and H0LiCOW values significantly differ from the Planck number of 67, strengthening the tension between Hubble constant measurements of the modern universe and the predicted value based on observations of the early universe.

One of the challenges we overcame was having dedicated monitoring programs through COSMOGRAIL to get the time delays for several of these quasar lensing systems, said Frdric Courbin of the Ecole Polytechnique Fdrale de Lausanne, leader of the COSMOGRAIL project.

Suyu added: At the same time, new mass modeling techniques were developed to measure a galaxys matter distribution, including models we designed to make use of the high-resolution Hubble imaging. The images enabled us to reconstruct, for example, the quasars host galaxies. These images, along with additional wider-field images taken from ground-based telescopes, also allow us to characterize the environment of the lens system, which affects the bending of light rays. The new mass modeling techniques, in combination with the time delays, help us to measure precise distances to the galaxies.

Begun in 2012, the H0LiCOW team now has Hubble images and time-delay information for 10 lensed quasars and intervening lensing galaxies. The team will continue to search for and follow up on new lensed quasars in collaboration with researchers from two new programs. One program, called STRIDES (STRong-lensing Insights into Dark Energy Survey), is searching for new lensed quasar systems. The second, called SHARP (Strong-lensing at High Angular Resolution Program), uses adaptive optics with the W.M. Keck telescopes to image the lensed systems. The teams goal is to observe 30 more lensed quasar systems to reduce their 2.4% percent uncertainty to 1%.

NASAs upcoming James Webb Space Telescope, expected to launch in 2021, may help them achieve their goal of 1% uncertainty much faster through Webbs ability to map the velocities of stars in a lensing galaxy, which will allow astronomers to develop more precise models of the galaxys distribution of dark matter.

The H0LiCOW teams work also paves the way for studying hundreds of lensed quasars that astronomers are discovering through surveys such as the Dark Energy Survey and PanSTARRS (Panoramic Survey Telescope and Rapid Response System), and the upcoming National Science Foundations Large Synoptic Survey Telescope, which is expected to uncover thousands of additional sources.

In addition, NASAs Wide Field Infrared Survey Telescope (WFIRST) will help astronomers address the disagreement in the Hubble constant value by tracing the expansion history of the universe. The mission will also use multiple techniques, such as sampling thousands of supernovae and other objects at various distances, to help determine whether the discrepancy is a result of measurement errors, observational technique, or whether astronomers need to adjust the theory from which they derive their predictions.

The team will present its results at the 235th meeting of the American Astronomical Society in Honolulu, Hawaii.

The Hubble Space Telescope is a project of international cooperation between the European Space Agency (ESA) and NASA. NASAs Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

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H0LiCOW! Cosmic Magnifying Glasses Yield Independent Measure of Universe's Expansion That Adds to Troubling Discrepancy - SciTechDaily

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