Cosmologists want to know how quickly the universe expands, but their results do not suit predictions. The red giant stars Wendy Freedman feels it can help.
For many years the big news in cosmology was the increasing proof that the universe expands more quickly than anticipated. As cosmologists extrapolate data from the early universe to estimate the present state of the cosmos, they expect a relatively slow rate of cosmic expansion. If you calculate specifically the rate at which celestial objects hurl away, you find that the room is about 9 percent faster than the prediction. The disparity may mean that our perception of the universe lacks anything fantastic.
Over the last year, he issue reached a crescendo. Last March, the principal cosmic expansion measurement group released its revised report, again at a rate of expansion far beyond expectations. Then in July a new measurement of cosmic growth using the objects known as quasars passed “five sigmas,” a statistical amount which is generally treated by physicists as the normal demonstration of an unreported physical effect, when coupled with the other measurement. In this case, cosmologists say, over and above dark matter, darkened energy and all else they include in their calculations may be an extra fundamental component that speeds up the universe.
But if the measurements are accurate, that is. A new line of evidence, first revealed in the summer, suggests that the rate of interstellar expansion can be much closer to the levels expected by early universe measurements and the traditional cosmological theory.
The expansion rate, known as the Hubble constant, was determined by Wendy Freedman, a distinguished cosmologist from Chicago University and Carnegie Observators, with stars she considered to be cleaner expansion probes. The TRGB-stars were used to obtain a significantly lower Hubble rate for her team compared with other observers.
While Freedman is known for her groundbreaking and careful research, some scientists reverted to their methods after last summer’s introduction. They argued that for part of their research and unknown techniques of calibration, their team used outdated data. The Critics believed that the Hubble value would grow and fit with other astronomical measurements if Freedman’s team used newer data.
That was not the case. Freedman’s team outlined its study of the TRGB stars in detail, summarized its accuracy checks and responded to criticisms, in a paper published online on February 5 and accepted for publication in The Astrophysical Journal. The new paper reports an ever-lasting rate of cosmic expansion that is much closer to the early-universe rate last summer. The more up-to-date details critics thought Freedman Hubble’s value would increase had the opposite effect. She said, “It made it come down.
The question of whether the universe grows faster than expected first emerged in 2013, when the Planck satellite correctly projected ancient microwaves from all directions into the atmosphere. The problem is with dust A thorough description of the early universe was discovered by the microwaves and from this the team of Planck could cause specific ingredients like dark matter in the cosmos. The ingredients were incorporated into Gravity Equations by Albert Einstein and allowed scientists to measure the predicted rate of expansion of space today, the final full study of which Planck produced 1 percent at 67.4 km per second per megaparse. In other words, when we look in space, astronomical bodies with every megaparsec distance fall from us 67,4 kilometers a second faster, just as dots on the inflating bullet disperse as soon as they are far apart.
But for some years Adam Riess, a cosmologist at Johns Hopkins University and recipient of the Nobel Prize for dark energy, had achieved higher value by calculating directly the rate of cosmic expansion. The trend continued; Riess ‘ team clamped the Hubble constant at 74 kilometers per second per megaparsec, 9 per cent higher than the 67.4 extrapolated in the early universe, according to their latest study last March.
The catch is that the Hubble constant is very difficult to measure. Astronomers such as Riess and Freedman first have to locate and calibrate “normal bowls:” astronomical bodies with a well-known distance and intrinsic luminosity. With these values in view, it is possible to determine the distances to fainter and further regular candles. Such distances then equate with how rapidly the objects travel, show the constant of Hubble.
As its regular candles, Riess and his team use pulsing stars called cepheids. The distances of stars can be determined using parallax and other tools, and pulsate with an intricately bright frequency. It allows astronomers, in distant galaxies that send them the distances of Type1a supernovas within these same galaxies to measure the relative distances from weak cephes — explosions that act as brighter but less common candles. These are used for calculating the distances to hundreds of far-off supernovas, the Hubble constant being the recession speed divided by their size.
The Riess Team Hubble 74 value was more impressive last year when the equivalent result of independent measurements using quasars was 73.3, measurements on the basis of what was known as masers landed at 73.9, and additional independent measures for quasars returned at 74.2.
However, Freedman has long been concerned about possible sources of error, who helped lead the way in the cepheid process currently used by Riess. Cepheids change when they are old, which is not ideal for conventional candles. Cephéids also have two negative effects in dense stellar regions: First, they are often filled with dust and block starlight, making objects look farther. Second, crowding can make them look sharper and therefore smaller than they do, which could lead to the Hubble constant being overestimated. And Freedman used the tip of the red giant stars in the branch.
TRGBs are what our sun’s stars are shortly before they die. They are slowly increasing in size as red giants until they reach a standard peak light due to the sudden helium combustion in their nuclei. Such red peak giants are always the same, making their candles standard; they often live on clean, sparsely-plated edges of galaxies instead of dusty and crowdy regions, as old stars. Barry Madore, Freedman husband and co-worker, also at the Chicago and the Carnegie Observatories, said “in simplicity, tip of the red giant bras wins hands down.’
The TRGB stars were first tested by Freedman, Madore and their team to see how bright they are from a known radius. Only then can they compare the brightness of TRGBs and supernovas farther away (and thus deduce the distance).
They picked TRGB stars in the Large Magellanic Cloud for their regular candles. The galaxy in their vicinity is known for their size. The large magellanic cloud is toxic, so that the luminosity of the stars can not be seen directly. The intrinsic brightness of the TRGBs in two other places was measured by Freedman and his staff: the galaxy IC 1613 and the Small-Magellanic Cloud. Their presence was essentially dust free (but not located exactly).
TRGBs in those pure areas are like the sun when they are high in the sky; TRGBs are like the sun near the horizon in the Large Magellanic Cloud, roddden and dimmed in the atmosphere by the dust. By comparing the star colors in dusty and clean areas, researchers may decide how much dust there is in the duby region. (Dust makes objects look redder because, ideally, blue light scatters) In Big Magellanic Cloud, they find that there is more dust than they thought before. This showed how much the dust dims stars, and therefore how luxurious they are, so that the stars can be used as standard candles.
A variety of other accuracy tests were performed independently on the relative distances between large and small magellanic clouds and the Galaxy IC 1613. The TRGB distance ladder produces a Hubble values of 69.6 well below the measurements of cephes, quasars and masers in the early universe results.