Astronomers improve cosmic distance scale with Hubble
April 11, 2007An international team of astronomers led by Fritz Benedict and Barbara McArthur of The University of Texas at Austin has used Hubble Space Telescope to solve one of the biggest problems in measuring the universe's expansion. Their results are published in the April issue of the Astronomical Journal.
The universe's rate of expansion, called "the Hubble constant," has been hotly debated for decades. It plays an important role in calculating the age and fate of the universe, and the understanding of how the universe evolved since the Big Bang.
To calculate the Hubble constant, astronomers must be able to measure precise distances to galaxies billions of light-years away. That capacity, in turn, is built on a series of measurement techniques in the so-called "cosmic distance ladder"—each of which allow astronomers to measure distances a little farther out into the universe.
One rung in the distance ladder is called a "Cepheid variable star." The light from these stars varies in a predictable way, which allows astronomers to know their distance. Benedict's team set out to calibrate these Cepheids, to make them a better distance indicator.
This study, which will be of great use to astronomers in many areas of study, was seen as so essential that it ranked first among more than 1,000 proposals for use of Hubble Space Telescope in 2003, when the project began.
Benedict's team used Hubble to directly measure the distance to 10 Cepheids in our Milky Way galaxy.
"Knowing their distances from an independent method, and then comparing that to the distance derived from the star's light variation, enabled us to calibrate Cepheids into perfect 'standard candles,'" said Tom Barnes of The University of Texas at Austin, the team's Cepheid expert.
The team followed these 10 stars for two years, measuring their apparent motion on the sky, called "parallax." For an easy demonstration of this phenomenon, hold up one finger in front of your face, and close one eye. Then switch eyes. The finger seems to jump, though it hasn't actually moved. That apparent motion is parallax.
First, Benedict's team measured each star's precise position. They did this again six months later, when Earth's (and HST's) vantage point had changed to the opposite side of the Sun. Like the test using your eyes to watch a finger, the stars' positions seemed to jump. But that jump is so small—the size of a quarter seen from 1,500 miles away—that it can only be measured with the Hubble Space Telescope. This level of precision cannot be achieved using a ground-based telescope.
With parallax measurements in hand, the team figured out exactly how the intrinsic light output of each of these stars varies over time. And because Cepheid variable stars all work the same way, they can apply this technique across the universe.
According to Benedict, "With this calibration, astronomers can deduce the distance to any galaxy in which a Cepheid can be detected."
McArthur notes that they tested the result on other galaxies, and it gives distances consistent with other methods.
"Applying this relationship to many and more distant galaxies should improve the accuracy of the Hubble constant," she said.
This science of measuring precise positions of objects on the sky is called "astrometry." The Hubble Space Telescope Astrometry Team was founded at The University of Texas at Austin long before the telescope launched in 1990, and helped design its Fine Guidance Sensors and ensure they would be useful for this kind of study.
"We've been cranking on this since 1977," Benedict said, "and as we tell our children, 'Practice makes perfect!' This result has excited me more than any in my 35-year career, and we will have more and better over the next five years."
In addition to Benedict, McArthur and Barnes, the international team for this research consisted of Michael E. Feast of The University of Cape Town, Thomas E. Harrison of New Mexico State University, Richard J. Patterson of The University of Virginia, John W. Menzies of the South African Astronomical Observatory, Jacob Bean of The University of Texas at Austin and Wendy L. Freedman of the Observatories of the Carnegie Institution of Washington.
Source: University of Texas at Austin
-
Hubble zooms in on a magnified galaxy
Feb 02, 2012 |
5 / 5 (13) |
11
-
How well can astronomers study exoplanet atmospheres?
Jan 31, 2012 |
not rated yet |
0
-
Astronomers find a dark matter galaxy far, far away
Jan 18, 2012 |
4.3 / 5 (9) |
8
-
Earliest-yet observation of August SN2011fe supernova nails it: Destroyed star was white dwarf
Jan 11, 2012 |
4.9 / 5 (7) |
7
-
Rare ultra-blue stars found in neighboring galaxy's hub
Jan 11, 2012 |
5 / 5 (4) |
0
-
Engineers build first sub-10-nm carbon nanotube transistor
Feb 01, 2012 |
4.9 / 5 (31) |
30
-
Something old, something new: Evolution and the structural divergence of duplicate genes
Jan 31, 2012 |
4.6 / 5 (7) |
1
-
The hidden nanoworld of ice crystals: Revealing the dynamic behavior of quasi-liquid layers
Jan 30, 2012 |
5 / 5 (3) |
1
-
Stock market network reveals investor clustering
Jan 27, 2012 |
3.9 / 5 (23) |
8
-
Of microchemistry and molecules: Electronic microfluidic device synthesizes biocompatible probes
Jan 26, 2012 |
5 / 5 (1) |
0
-
Never ending outer space.....
3 hours ago
-
Neutron Star fragments?
5 hours ago
-
stationary or not?
9 hours ago
-
Scale of the Universe
Feb 10, 2012
-
Titan's lack of impact craters
Feb 09, 2012
-
Real pictures of black hole eating a star?
Feb 08, 2012
- More from Physics Forums - General Astronomy
More news stories
Europe stakes billion-dollar bet on new rocket
A pencil-slim rocket is scheduled to lift into space from South America on Monday, carrying a billion-dollar bet that Europe can grab a juicy slice of the market to place satellites in low orbit.
Space & Earth / Space Exploration
16 hours ago |
3.5 / 5 (2) |
0
Political leaders play key role in how worried Americans are by climate change: study
More than extreme weather events and the work of scientists, it is national political leaders who influence how much Americans worry about the threat of climate change, new research finds.
Feb 06, 2012 |
5 / 5 (6) |
72
NASA budget will axe Mars deal with Europe: scientists
US President Barack Obama's budget proposal to be submitted next week for 2013 will cut NASA's budget by 20 percent and eliminate a major partnership with Europe on Mars exploration, scientists said Thursday.
Space & Earth / Space Exploration
Feb 10, 2012 |
5 / 5 (3) |
48
Humans may have helped the decline of African rainforests 3000 years ago
(PhysOrg.com) -- Large areas of rainforests in Central Africa mysteriously disappeared over three thousand years ago, to be replaced by savannas. The prevailing theory has been that the cause was a change ...
Could Venus be shifting gear?
(PhysOrg.com) -- ESAs Venus Express spacecraft has discovered that our cloud-covered neighbour spins a little slower than previously measured. Peering through the dense atmosphere in the infrared, the ...
Space & Earth / Space Exploration
Feb 10, 2012 |
5 / 5 (8) |
10
|
Walney offshore wind farm is world's biggest (for now)
(PhysOrg.com) -- The Walney wind farm on the Irish Sea--characterized by high tides, waves and windy weather--officially opened this week. The farm is treated in the press as a very big deal as the Walney ...
GPS court ruling leaves US phone tracking unclear
A US Supreme Court decision requiring a warrant to place a GPS device on the car of a criminal suspect leaves unresolved the bigger issue of police tracking using mobile phones, legal experts say.
Europeans protest controversial Internet pact
Tens of thousands of people marched in protests in more than a dozen European cities Saturday against a controversial anti-online piracy pact that critics say could curtail Internet freedom.
Study finds that anti-diabetic medication can prevent the long-term effects of maternal obesity
In a study to be presented today at the Society for Maternal-Fetal Medicine's annual meeting, The Pregnancy Meeting, in Dallas, Texas, researchers will report findings that show that short therapy with the anti-diabetic medication ...
Netflix settlement trims 14 pct off 4Q earnings
(AP) -- Netflix pressed the rewind button on its fourth-quarter earnings after settling allegations that the video subscription service violated a consumer-privacy law.
Navy to begin tests on electromagnetic railgun prototype launcher
The Office of Naval Research (ONR)'s Electromagnetic (EM) Railgun program will take an important step forward in the coming weeks when the first industry railgun prototype launcher is tested at a facility ...