Spitzer Provides Most Precise Measurement Yet of the Universe’s Expansion

This graph illustrates the Cepheid period-luminosity relationship, which scientists use to calculate the size, age and expansion rate of the Universe. Credit: NASA/JPL-Caltech/Carnegie

How fast is our Universe expanding? Over the decades, there have been different estimates used and heated debates over those approximations, but now data from the Spitzer Space Telescope have provided the most precise measurement yet of the Hubble constant, or the rate at which our universe is stretching apart. The result? The Universe is getting bigger a little bit faster than previously thought.

The newly refined value for the Hubble constant is 74.3 plus or minus 2.1 kilometers per second per megaparsec.

The most previous estimation came from a study from the Hubble Space Telescope, at 74.2 plus or minus 3.6 kilometers per second per megaparsec. A megaparsec is roughly 3 million light-years.

To make the new measurements, Spitzer scientists looked at pulsating stars called cephied variable stars, taking advantage of being able to observe them in long-wavelength infrared light. In addition, the findings were combined with previously published data from NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) on dark energy. The new determination brings the uncertainty down to 3 percent, a giant leap in accuracy for cosmological measurements, scientists say.

WMAP obtained an independent measurement of dark energy, which 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 Nobel Prize in physics.

The Hubble constant is named after the astronomer Edwin P. Hubble, who astonished the world in the 1920s by confirming our universe 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 expansion rate is critical for understanding the age and size of the universe.

“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 Hubble Space Telescope study that earlier had measured the Hubble constant.

Glenn Wahlgren, Spitzer program scientist at NASA Headquarters in Washington, said the better views of cepheids enabled Spitzer to improve on past measurements of the Hubble constant.

“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.”

“Spitzer is yet again doing science beyond what it was designed to do,” said project scientist Michael Werner at NASA’s Jet Propulsion Laboratory. 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.”

The study appears in the Astrophysical Journal.

Paper on arXiv: A Mid-Infrared Calibration of the Hubble Constant

Source: JPL

18 Replies to “Spitzer Provides Most Precise Measurement Yet of the Universe’s Expansion”

  1. Erm, can someone explain to me what “74.3 plus or minus 2.1 kilometers per second per megaparsec.” actually means?
    The ‘per megaparsec’ bit has thrown me….
    Love the site, btw.

  2. “The Universe is getting bigger a little bit faster than previously thought.”

    Looking at both plus-minuses that statement is kinda strange to me. 0.1 difference and it could be wrong for as much as 2.1 km. It feels like a sharper confirmation.

  3. Well, basically, if a galaxy is 1 megaparsec distant from us (about 3.26 million light-years), the expansion of space would carry it along at 74.3 km/sec; if a galaxy is 2 megaparsecs distant, it would be appear to be travelling away at 148.6 km/sec; if a galaxy is 3 megaparsecs distant, it would appear to be travelling away at 222.9 km/sec, and so on. In other words, the farther away they are, the faster they appear to be moving – it’s the rate of that expansion which was measured.

    1. Is there anything in the universe so far away from us, that it would appear to be moving faster than the speed of light?

      1. Although objects in the universe are constrained by special relativity from moving faster than the speed of light, there is no such theoretical constraint when space itself is expanding; therefore, it is possible for two very distant objects to be expanding away from each other at a combined speed greater than the speed of light, and this is the case for any object that is more than approximately 4.2 gigaparsecs (13.7 billion light-years) away from us. Such objects can still be observed because the universe in the past was expanding more slowly than it is today, so the ancient light being received from these objects is still able to reach us; however, if the expansion of space continues unabated as the model extrapolations presume, we will never get to see the light being emitted from those objects today.

      2. Thanks for the answer! I find that very fascinating, although the universe being approximately 13.7 billion years old (is that just a coincidence?), I suppose there aren’t many objects right now that are expandind faster than light from us.

  4. “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
    Factor of 2 just over 10 years ago? Surely not. I thought we had it nailed to around 14 billion years old much longer ago than that.

    1. Not an expert, but there were a factor 2 involved:

      “The first reasonably accurate measurement of the rate of expansion of the Universe, a numerical value now known as the Hubble constant, was made in 1958 by astronomer Allan Sandage.[17] His measured value for the Hubble constant yielded the first good estimate of the age of the Universe, coming very close to the value range generally accepted today.
      However Sandage, like Einstein, did not believe his own results at the time of discovery. His value for the age of the Universe was too short to reconcile with the 25-billion-year age estimated at that time for the oldest known stars. Sandage and other astronomers repeated these measurements numerous times, attempting to reduce the Hubble constant and thus increase the resulting age for the Universe. Sandage even proposed new theories of cosmogony to explain this discrepancy. This issue was finally resolved by improvements in the theoretical models used for estimating the ages of stars.”

  5. The age of the Universe is about 13.75 billion years; however, due to the expansion of space, we are observing the most distant objects in the Universe that were originally about 13 billion light-years away, but are now at a much farther distance from our observation point – putting the edge of the observable universe at about 46–47 billion light-years away!

    1. Thanks for the reply.
      Now, the next question; why is the universe expanding at different speeds?

    1. Two dislikes?! WTF?! Did I upset the sensibilities of some bloody creationists or “Electric Universe” nutters here, or what?

  6. As in so many areas, fortunate for man, that these “standard candles” exist out-there in the dark of night. Huge, yellow, bulging Supergiant stars(?), yet shining with such a predictable regularity(?) of pulse, and intensity of light (as if computer-controlled), that we can use them to gauge cosmological(?) measures of distance. Without their quantifiable light, we might be left adrift in the night, missing a sextant to plot our position in the ocean of space, from lines of measured time. Advancement over brighter seas of knowledge, and into deeper waters of understanding, might have been a lot harder, if not impossible.

    Judging distance by receding light of a candle bearer, was vividly helpful for this non-scientist. Without such a reliable frame of reference, can you really adequately find your bearings, locate your true-position on the higher scales of magnitude, in relation to the greater surroundings? Absent any other, might you become “geographically” disoriented, or even lost on the four-dimensional space map, unable to gauge true-distance, or judge actual time-zones, place-locations, and the measured distances between them? ____________________________________________

    Like an inverse process of Cosmic inflation, one brilliant flash-point of beginning, the expanding progress of Science appears to be accelerating towards a focal-point climax of illuminating-realization: A defining moment of intensely concentrated recognition, when all the intersecting perimeters of energy-mater and space-time, the unseen forces, and emerging atomic structures, …, will powerfully, suddenly (with a seismic shudder) fuse-together into one astonishingly awesome, beautifully elegant, yet magnificently simple “unified field theory” of grand design! One overwhelming, radiant-point of clarity, may be the ultimate coruscating convergence of these narrowing lines of research. What a humbling moment that concentrated singularity of recognition could be for the generation that manages to to reach that supreme locus (if ever). Those who were privileged to have continued man’s ancient quest to know his Cosmic place, and understand the grand scheme of his World, to search over horizons of explored seas, to follow prevailing winds out under unfamiliar stars, and steer by favorable currents into the far-recesses of the unknown.

  7. Once we know that universe is expanding at a more or less precise speed, one issue that intrigues me is if we reverse that expansion we should be able to find a point in space which is the origin of that expansion. It would be curious to find the location of that point in space…

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