The Universe Is Expanding Way Faster Than We Thought, Researchers Say

                                                                        

The Universe is expanding. In the standard model of cosmology the rate of that expansion is given by the Hubble parameter, which is a measure of the dark energy that drives cosmic expansion. New observations of distant galaxies yield a higher than expected Hubble value. That may mean the Universe is expanding faster than we thought, but there’s no need to start rewriting textbooks just yet.

Since the Hubble parameter measures the rate of cosmic expansion, one way to determine it is to compare the redshift of light from distant galaxies with their distance. The cosmological redshift of a galaxy is easy to measure, and is due to the fact that cosmic expansion stretches the wavelength of light as it travels across millions or billions of light years, making it appear more red. By comparing the redshifts for galaxies of different distances we can determine just how fast the Universe is expanding.

Unfortunately distance is difficult to determine. It relies upon a range of methods that vary depending on distance, known as the cosmic distance ladder. For close stars we can use parallax, which is an apparent shift of stars relative to more distant objects due to the Earth’s motion around the Sun. The greater a star’s distance the smaller its parallax, so the method is only good to about 1,600 light years. For larger distances we can look at variable stars such as Cepheid variables. We know the distance to some Cepheid variables from their parallax, so we can determine their actual brightness (absolute magnitude). From this we’ve found that the rate at which a Cepheid variable changes in brightness correlates with its overall brightness. This relation means we can determine the absolute brightness of Cepheid variables greater than 1,600 light years away. 

If we compare that to their apparent brightness we can calculate their distance. By observing Cepheids in various galaxies we can determine galactic distances. We can observe Cepheids out to about 50 million light years, at which point they’re simply too faint to currently observe.

The achilles heel of the cosmological distance ladder is that it relies upon a chain of data. The distance for supernovas depends upon the calculated distance of Cepheid variables, which in turn depend upon parallax distance measurements. With ever increasing distance comes greater uncertainty in the results.

So you want your uncertainties at each step to be as small as possible, which is where this new work comes in. Using data from the Hubble Space Telescope’s Wide Field Camera 3, a team TISI +% measured about 2,400 Cepheid variables in 11 galaxies where a Type Ia supernova had also occurred. This allowed them to reduce the uncertainty of supernova distance measurements. They then compared the distances and redshifts for 300 supernovae to get a measure of the Hubble parameter accurate to within 2.4%.

That by itself is good work, but the result was surprising. 

The value for the Hubble parameter they got was about 73 km/s per megaparsec, which is higher than the “accepted” value of 69.3. The difference is large enough that it falls outside the uncertainty range of the accepted value. If the result is right, then it means the Universe is expanding at a faster rate than we thought. It could also point to an additional dark energy component in the early Universe, meaning that dark energy is very different than we’ve supposed.

But we shouldn’t consider this result definitive just yet. 

The use of supernovae to measure the Hubble parameter isn’t the only method we have. We can also look at the way galaxies cluster on large scales, and fluctuations in the cosmic microwave background. Each of these gives a slightly different value for the Hubble parameter, and the “accepted” value is a kind of weighted average of all measurements. 

The variation of values from different methods is known as tension in the cosmological model, and any new claim about dark energy and cosmic expansion will need to address this tension. If the supernova method is right and the Universe really is expanding faster than we thought, why do other methods yield a value significantly smaller than the true value?

It could be that there is some bias in one or both of the methods that we haven’t accounted for. Planck, for example, has to account for gas and dust between us and the cosmic background, and that may be skewing the results. It could be that the supernovae we use as standard candles to measure galactic distance aren’t as standard as we think. It could also be that our cosmological model isn’t quite right. 

The current model presumes that the universe is flat, and that cosmic expansion is driven by a cosmological constant. We have measurements to support those assumptions, but if they are slightly wrong that could account for the differences as well.

This new result does raise interesting questions, and it confirms that the discrepancy between different methods is very real. Whether that leads to a new understanding of cosmic expansion and dark energy is yet to be seen.

Paper: Adam G. Riess, et al. A 2.4% Determination of the Local Value of the Hubble Constant. arXiv:1604.01424 [astro-ph.CO] (2016)

By Brian Koberlein who is an astrophysicist, professor and author. You can find more of his writing at One Universe at a Time.

With many thanks to Forbes

Oldest Stars in the Universe Found Near Milky Way Centre: Study

                                                                        

Astronomers have discovered what they believe to be the oldest stars ever seen, dating from before the Milky Way Galaxy formed, when the universe was just 300 million years old.

The nine stars, found near the centre of the Milky Way, are surprisingly pure but contain material from an even earlier star, which died in an enormous explosion called hypernova, the researchers noted.

"These pristine stars are among the oldest surviving stars in the Universe, and certainly the oldest stars we have ever seen," said , lead author of the study Louise Howes from The Australian National University (ANU).

"These stars formed before the Milky Way, and the galaxy formed around them," Howes explained.

The discovery and analysis of the nine pure stars challenges current theories about the environment of the early universe from which these stars formed.

"The stars have surprisingly low levels of carbon, iron and other heavy elements, which suggests the first stars might not have exploded as normal supernovae," Howes noted.

"Perhaps they ended their lives as hypernovae - poorly understood explosions of probably rapidly rotating stars producing 10 times as much energy as normal supernovae," Howes said.

Finding such rare relic stars amongst the billions of stars in the Milky Way centre was like finding a needle in a haystack, project leader professor Martin Asplund, from ANU explained.

"The ANU SkyMapper telescope has a unique ability to detect the distinct colours of anaemic stars - stars with little iron - which has been vital for this search," Asplund pointed out.
Following the team's discovery in 2014 of an extremely old star on the edge of the Milky Way, the team focused on the dense central parts of the galaxy, where stars formed even earlier.

The team sifted through about five million stars observed with SkyMapper to select the most pure and therefore oldest specimens, which were then studied in more detail using the Anglo-Australian Telescope near Coonabarabran in New South Wales and the Magellan telescope in Chile to reveal their chemical make-up.

The discovery was reported in the journal Nature.

With many thanks to NDTV

Stunning 3-D Animations of Hubble’s Universe

                                                                     

                                                                        

The talented astronomical artists at the Space Telescope Science Institute have been pouring the gorgeousness of Hubble pictures into our eyes and brains for years. They recently embarked on a new venture: Taking those same images and, using complementary data to get more information about the objects, creating stunning 3-D animations. Mind you, these are not “real,” but visualizations based on actual data that approximate the view you’d have if you could fly around the Universe at multiple times the speed of light.

Here’s one they made of one of my all-time favorite celestial sites, Sharpless 2-106, the birthplace of a massive star:

Note: I added the notes and the music.

I’ve written about SH 2-106 a few times because it’s a fascinating object as well as one of the most beautiful images Hubble has produced. While this animation isn’t exactly real, it does give you a sense that you’re seeing a huge star that’s carved out tremendous cavities in the surrounding gas.

That’s difficult to see in the usual two-dimensional static images, so while these visualizations are in some ways flights of fancy, I think they provide a useful tool to better understand astronomical objects.

There are several more videos like this at hubblesite.org, so I urge you to go take a look. They’re quite lovely.

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death from the Skies! Follow him on Twitter.

With many thanks to Slate

NASA Discovers 715 New Planets

                                                       

                                                                    
                                                                    
                                                                     

Our galactic neighborhood just got a lot bigger. NASA on Wednesday announced the discovery of 715 new planets, by far the biggest batch of planets ever unveiled at once.

By way of comparison, about 1,000 planets total had been identified in our galaxy before Wednesday.

Four of those planets are in what NASA calls the "habitable zone," meaning they have the makeup to potentially support life.

The planets, which orbit 305 different stars, were discovered by the Kepler space telescope and were verified using a new technique that scientists expect to make new planetary discoveries more frequent and more detailed.

"We've been able to open the bottleneck to access the mother lode and deliver to you more than 20 times as many planets as has ever been found and announced at once," said Jack Lissauer, a planetary scientist at NASA's Ames Research Center in California.

Launched in March 2009, the Kepler space observatory was the first NASA mission to find planets similar to Earth that are in, or near, habitable zones -- defined as planets that are the right distance from a star for a moderate temperature that might sustain liquid water.

Tuesday's planets all were verified using data from the first two years of Kepler's voyage, meaning there may be many more to come.

"Kepler has really been a game-changer for our understanding of the incredible diversity of planets and planetary systems in our galaxy," said Douglas Hudgins, a scientist with NASA's astrophysics division.

The new technique is called "verification by multiplicity," and relies in part on the logic of probability. Instead of searching blindly, the team focused on stars that the technique suggests are likely to have more than one planet in their orbit.

NASA says 95% of the planets discovered by Kepler are smaller than Neptune, which is four times as big as Earth.

One of them is about twice the size of Earth and orbits a star half the size of Earth's sun in a 30-day cycle.

The other three planets in habitable zones also are all roughly twice the size of Earth. Scientists said the multiplicity technique is biased toward first discovering planets close to their star and that, when further data comes in, they expect to find a higher percentage of new planets that could potentially have a life-supporting climate like Earth's.

"The more we explore the more we find familiar traces of ourselves amongst the stars that remind us of home," said Jason Rowe, a research scientist at the SETI Institute in Mountain View, California, and co-leader of the research team.

By Doug Gross

                                                       

With thanks to CNN. More information and pictures there.

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