Accurate measurement of the Hubble constant, a value that describes how the universe is expanding rapidly, has been forbidden by scientists for decades. Lowering that number would lead to a lengthy discussion among astronomers to rest us and bring us one step closer to understanding the evolution and destiny of the universe. Researchers have now used the latest discovery of gravity waves to present evidence of the concept of a completely new method of determining the constant.
So far astronomers have taken two approaches to calculate the constant value. One method uses known brightness objects, called standard candles, such as Cepheid Variable Stars. The light of Cepheid's stars fluctuates at regular intervals, and the interval is associated with the amount of light it emits. Performing the real stars' brightness from its speed of fluctuation and comparing it with what the observers see as plain astronomers determine its distance. Scientists then measure the red shift of the same objects – that is, how much light shifted towards the red end of the electromagnetic spectrum. A red shift occurs when the source of light moves away from the observer; the light waves emitted from it will be stretched. This is similar to the sound of a siren car falling in height as the vehicle is driving. Measuring the red shift of a distant star, astronomers can calculate how fast they move away from Earth. When they combine that information with its distance, the value of the Hubble constant is obtained.
The second technique for determining the velocity of space expansion relies on the cosmic microwave background (CMB), ghostly radiation remaining from a large burst pervading deep space. Precise measurements of temperature variations in CMB from Planck's Space Telescope, when included in a standard high-beam cosmology model, allow astronomers to perform a constant.
The problem is that the values derived from these methods do not agree – the disagreement that cosmologists call "tension". CMB estimates are closer to 68. Most researchers first thought that this difference could be the result of error measurements (which astrophysicists knew as "systematic"). But despite years of research, scientists can not find enough bigger sources of error to explain that gap.
The more exciting possibility is that tension reflects the real difference between the Hubble constant at the distance Planck sees, far from the early universe, and the standard candle methods of the nearby, recent universe. Of course, scientists already know that expanding the universe is accelerating – though they do not know exactly why they call it the mysterious cause of "dark energy".
But even considering the known acceleration, tension suggests that something strange can happen to dark energy to keep the Hubble constant so far off. This indicates the speed of expansion during the cosmic epoch following a major burst, which CMB would reflect, was radically different from what cosmologists currently consider. If dark anomalies are not the fault, it is possible that some unknown particles such as undiscovered neutrino flavors, almost silent particles pervading the universe, will affect the calculations. "This tension can hide the solution of the universe's description of its evolution, the sources of energy contained in it," says Valeria Pettorino, astrophysicist and researcher at CEA Saclay in France, who was not involved in the study. "And in practice, it determines the past, the present, and the future of our universe, regardless of whether it will expand forever, regardless of whether it will collapse again and recover."
Waves in space-time
Now, using the gravitational wave signals from joining two black holes and red shift data from one of the most ambitious surveys ever conducted, researchers have developed a brand new way of calculating the Hubble constant. They described the method in the study they were subjected to Astrophysical letters of the journal and August 6, on the pages of the preface arXiv. It reports values of 75.2 for the constant, though with a large error limit (+39.5, -32.4, which means that the actual number could be up to 114.7 or be low) as 42.8). This great uncertainty reflects the fact that the calculation comes from one measurement and hence does not help to illuminate the tension between the two original calculation methods. But as evidence of the concept, the technique is revolutionary. Just another measurement, from October 2017, attempted to calculate the Hubble constant using gravity waves. Scientists hope that the discovery of the gravity wave will help improve the precision of the calculations.
Gravity waves are waves in space-time tissue. Einstein's general theory of relativity predicted their existence in 1915, and astronomers have since found ways to discover them. It is not surprising that the collapse of massive objects creates a significant plague of gravity waves. In 1986, physicist Bernard Schutz first proposed the so-called " Binary systems that could be used to determine the Hubble constant. He claimed that the observatory would likely be discovered in the near future; in fact, it took nearly 30 years before observers saw the signals.
The Laser Interferometric Observatory with Luminous Waves (LIGO) in Louisiana and Washington has made the first discovery of the world's gravitational waves in September 2015 and has since seen less than a dozen events, along with a European counterpart, Virgin. Experiments seek miniature changes in space-time caused by the passing of gravity waves.
The scattering of gravity waves from the merging of two black holes is part of a new method for calculating the Hubble constant. Unlike standard candles, binary systems of black holes oscillate. As they spiral into each other, the frequency of gravitational waves exits changes at a rate that is related to the size of the system. Hence, astronomers perform the internal amplitude of the waves. By comparing them with their apparent amplitude (similar to the comparison of the real brightness of Cephas with its apparent light), they calculate how far the system is. Astronomers call these "standard sirens". Measured distance to this particular collision is about 540 megaparsek, or about 1.8 billion light years, from Earth.
The associated red shift, as is the case with the siren host galaxy, provides the second part of the new method. Researchers used the red shift data from the Dark Energy Survey, who has just finished mapping a part of the southern sky wider and deeper than any previous research. Red shift data combined with distance measurement provided researchers with a new number for the constant.
Antonella Palmese, a research associate at Fermilab and co-author of the study, says the method promises partly because the black holes are relatively rich. Although this is still a proof of the concept, she says that, given that LIGO / VIRGO will have more gravitational events, statistics will improve. Oxford University astronomer Elisa Chisari, who was not involved in the study, agrees with that. "The level of constraints at the Hubble rate is currently not competitive compared to other measurements," she says. "However, since LIGO builds a catalog of gravity wave events in the coming years, combining multiple events will really become a competitive method."