Infrared observatory measures expansion of universe

Oct 03, 2012
Astronomers using NASA's Spitzer Space Telescope have greatly improved the cosmic distance ladder used to measure the expansion rate of the universe, as well as its size and age. The cosmic distance ladder, symbolically shown here in this artist's concept, is a series of stars and other objects within galaxies that have known distances. Credit: NASA/JPL-Caltech

(Phys.org)—Astronomers using NASA's Spitzer Space Telescope have announced the most precise measurement yet of the Hubble constant, or the rate at which our universe is stretching apart.

The Hubble constant is named after the astronomer Edwin P. Hubble, who astonished the world in the 1920s by confirming our has been expanding since it exploded into being 13.7 billion years ago. In the late 1990s, astronomers discovered the expansion is accelerating, or speeding up over time. Determining the is critical for understanding the age and size of the universe.

Unlike NASA's Hubble , which views the cosmos in visible light, Spitzer took advantage of long-wavelength infrared light to make its new measurement. It improves by a factor of 3 on a similar, seminal study from the and brings the uncertainty down to 3 percent, a giant leap in accuracy for cosmological measurements. The newly refined value for the Hubble constant is 74.3 plus or minus 2.1 kilometers per second per megaparsec. A megaparsec is roughly 3 million light-years.

"Spitzer is yet again doing science beyond what it was designed to do," said project scientist Michael Werner at NASA's Jet Propulsion Laboratory in Pasadena, Calif. Werner has worked on the mission since its early concept phase more than 30 years ago. "First, Spitzer surprised us with its pioneering ability to study exoplanet atmospheres," said Werner, "and now, in the mission's later years, it has become a valuable cosmology tool."

In addition, the findings were combined with published data from NASA's to obtain an independent measurement of , one of the greatest mysteries of our cosmos. Dark energy is thought to be winning a battle against gravity, pulling the fabric of the universe apart. Research based on this acceleration garnered researchers the 2011 .

This graph illustrates the Cepheid period-luminosity relationship, which scientists use to calculate the size, age and expansion rate of the universe. The data shown are from NASA's Spitzer Space Telescope, which has made the most precise measurements yet of the universe's expansion rate by recalculating the distance to pulsating stars called Cepheids. Credit: NASA/JPL-Caltech/Carnegie

"This is a huge puzzle," said the lead author of the new study, Wendy Freedman of the Observatories of the Carnegie Institution for Science in Pasadena. "It's exciting that we were able to use Spitzer to tackle fundamental problems in cosmology: the precise rate at which the universe is expanding at the current time, as well as measuring the amount of dark energy in the universe from another angle." Freedman led the groundbreaking study that earlier had measured the Hubble constant.

Glenn Wahlgren, Spitzer program scientist at NASA Headquarters in Washington, said infrared vision, which sees through dust to provide better views of variable stars called cepheids, enabled Spitzer to improve on past measurements of the .

"These pulsating stars are vital rungs in what astronomers call the cosmic distance ladder: a set of objects with known distances that, when combined with the speeds at which the objects are moving away from us, reveal the expansion rate of the universe," said Wahlgren.

Cepheids are crucial to the calculations because their distances from Earth can be measured readily. In 1908, Henrietta Leavitt discovered these stars pulse at a rate directly related to their intrinsic brightness.

To visualize why this is important, imagine someone walking away from you while carrying a candle. The farther the candle traveled, the more it would dim. Its apparent brightness would reveal the distance. The same principle applies to cepheids, standard candles in our cosmos. By measuring how bright they appear on the sky, and comparing this to their known brightness as if they were close up, astronomers can calculate their distance from Earth.

Spitzer observed 10 cepheids in our own Milky Way galaxy and 80 in a nearby neighboring galaxy called the Large Magellanic Cloud. Without the cosmic dust blocking their view, the Spitzer research team was able to obtain more precise measurements of the stars' apparent brightness, and thus their distances. These data opened the way for a new and improved estimate of our universe's expansion rate.

"Just over a decade ago, using the words 'precision' and 'cosmology' in the same sentence was not possible, and the size and age of the universe was not known to better than a factor of two," said Freedman. "Now we are talking about accuracies of a few percent. It is quite extraordinary."

The study appears in the Astrophysical Journal.

Explore further: Image: Chandra's view of the Tycho Supernova remnant

More information: dx.doi.org/10.1088/0004-637X/758/1/24

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dtyarbrough
1 / 5 (13) Oct 03, 2012
The problem with cepheids it that scientists believe that brightness is only distance related. If they are dimmer than expected, they must be farther away. If they are dimmer than before, they must must be moving farther away. The sun is pumping out solar material in the solar wind that never leaves the solar system. Calculate the kilometers in a megaparsec. The sun is adding 74.3 plus or minus 2.3 particles per second for every 30,856,775,800,000,000,000 existing particles. This dims our view of the universe. Why else would we appear to be the center of the expansion? 1 parsec = 30,856,775,800,000 kilometers. At this rate, the sun will appear 1/2 km farther away in 100 years.

Q-Star
4.4 / 5 (20) Oct 03, 2012
The problem with cepheids it that scientists believe that brightness is only distance related. If they are dimmer than expected, they must be farther away.


Well duh! That's what they are trying to tell ya

If they are dimmer than before, they must must be moving farther away.


Duh again!

The sun is adding 74.3 plus or minus 2.3 particles per second for every 30,856,775,800,000,000,000 existing particles.


Are ya a drinking man? Those are some pretty outlandish numbers.

Why else would we appear to be the center of the expansion?


We don't appear to be the center of expansion. (The first principle.)

1 parsec = 30,856,775,800,000 kilometers. At this rate, the sun will appear 1/2 km farther away in 100 years.


I thought that was the number of particles you were trying count. Please promise to never, ever, help your kids with their homework. That would be considered child abuse.
SDrapak
2 / 5 (5) Oct 03, 2012
Everything is at the center of expansion because everything is expanding from everything else (more or less, not really locally)
Though you do have to wonder about their calculations. If light extinction is happening as the light from the cephids is travelling towards us (and we're finding there is an awful lot of material out there between the stars), the further they are away, the dimmer they would be on top of results from just the inverse square law of light. This would skew the results with further star seeming even further away than they really are.
Q-Star
4.1 / 5 (14) Oct 03, 2012
If light extinction is happening as the light from the cephids is travelling towards us (and we're finding there is an awful lot of material out there between the stars), the further they are away, the dimmer they would be on top of results from just the inverse square law of light.


You are quite correct, but that has been known for a long time.

This would skew the results with further star seeming even further away than they really are.


The photometric analysis is done in tandem with spectroscopic analysis. It takes into account of the matter which is in between the source and the detector. It's not an exact science to be sure, but unlike a biologist or a geologist or a chemist, we can't lay our hands on the thing we are investigating. We can't manipulate our subject. What we see, is all we get. We have to rely on what what we see. And that only at great distances.

But we have come a long way in the last 100 years. The last 20 have been a truly golden age.
Neurons_At_Work
5 / 5 (10) Oct 03, 2012
SDrapak--2 points: First, you are correct that the 'stuff' between the stars and ourselves could potentially skew the results, which is why the Spitzer is so valuable for this type of study--seeing in the IR helps cut through the dust which might obscure visible light observations. Second, note the line chart above. There is a fairly direct and predictable relationship between the periodicity of the Cepheids and their intrinsic luminosity. So, if we can measure the cyclic variations in brightness over time, even if the relative observed brightness is in question, we can then infer actual brightness based solely on the period.
yash17
1 / 5 (9) Oct 04, 2012
Expanding?
It is only a mirror effect.
DarkHorse66
3 / 5 (2) Oct 04, 2012
"If they are dimmer than before, they must must be moving farther away." Are trying to say that a change of location is the only factor that can cause a change in brightness of a star? You seem to forget that a star is not a passive & unchanging entity.The inside of ANY star is a maelstrom of activity & the very levels of activity are replete with fluctuations.
http://www.spacea...star.htm
Of course this is going to result in different brightness over time.Here is another page from the same site:
http://www.spacea...star.htm#obs
Notice that a variable star dims & brightens in CYCLES.If you take a look at some of the periods given in the table & try to fit that into your personal theory,your stars would not only be going backwards & forwards very fast indeed,they would be travelling in mini-CIRCLES around some individual separate central point to achieve these.Epi-cycles like these are pretty unlikely!Regards,DH66
DarkHorse66
3.7 / 5 (3) Oct 04, 2012
"The problem with cepheids it that scientists believe that brightness is only distance related." It's not quite THAT simple. From another page on the same site:
http://www.spacea...m#vclass

"Cepheids as Distance Markers

During her investigations of Cepheids in the Magellanic Clouds, astronomer Leavitt found a relationship between the period and the absolute brightness of a Cepheid (early 20th century).
The longer the period of a Cepheid, the greater was its absolute brightness.
Thus by measuring the period of a Cepheid we immediately know its absolute brightness. We can also measure its apparent brightness and thus calculate how far it is away from us. ( B = Bo / d2 )
Cepheids thus play a very important role as one of the ways to determine astronomical distance.
Because of this, Cepheids are referred to as standard candles."

Note the distinction between APPARENT & ABSOLUTE brightness.
Best Regards, DH66
Fleetfoot
5 / 5 (5) Oct 04, 2012
IMO the space-time doesn't expand, the light just becomes reddish with distance due its scattering with vacuum density fluctuations. .. This model leads into many testable predictions,..


In particular it predicts that the effect must be dependent on the wavelength. That has been carefully tested and does not occur hence the scattering model is ruled out.
Fleetfoot
5 / 5 (5) Oct 04, 2012
The problem with cepheids it that scientists believe that brightness is only distance related. If they are dimmer than expected, they must be farther away.


There is a secondary effect but generally that is correct.

If they are dimmer than before, they must must be moving farther away.


No, we cannot observe them long enough to judge speed by the rate of change of magnitude.

The sun is pumping out solar material in the solar wind that never leaves the solar system. .. This dims our view of the universe.


It is essentially transparent but your argument is flawed anyway, at any given time, the effect is the same for all cepheids so the slope of the line relating apparent magnitude to distance is independent of local dimming. Any effect within the Solar System would only move the entire line up a little, it wouldn't change the slope.