Nav: Home

Hubble makes the first precise distance measurement to an ancient globular star cluster

April 04, 2018

Astronomers using NASA's Hubble Space Telescope have for the first time precisely measured the distance to one of the oldest objects in the universe, a collection of stars born shortly after the big bang.

This new, refined distance yardstick provides an independent estimate for the age of the universe. The new measurement also will help astronomers improve models of stellar evolution. Star clusters are the key ingredient in stellar models because the stars in each grouping are at the same distance, have the same age, and have the same chemical composition. They therefore constitute a single stellar population to study.

This stellar assembly, a globular star cluster called NGC 6397, is one of the closest such clusters to Earth. The new measurement sets the cluster's distance at 7,800 light-years away, with just a 3 percent margin of error.

Until now, astronomers have estimated the distances to our galaxy's globular clusters by comparing the luminosities and colors of stars to theoretical models, and to the luminosities and colors of similar stars in the solar neighborhood. But the accuracy of these estimates varies, with uncertainties hovering between 10 percent and 20 percent.

However, the new measurement uses straightforward trigonometry, the same method used by surveyors, and as old as ancient Greek science. Using a novel observational technique to measure extraordinarily tiny angles on the sky, astronomers managed to stretch Hubble's yardstick outside of the disk of our Milky Way galaxy.

The research team calculated NGC 6397's age at 13.4 billion years old. "The globular clusters are so old that if their ages and distances deduced from models are off by a little bit, they seem to be older than the age of the universe," said Tom Brown of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, leader of the Hubble study.

Accurate distances to globular clusters are used as references in stellar models to study the characteristics of young and old stellar populations. "Any model that agrees with the measurements gives you more faith in applying that model to more distant stars," Brown said. "The nearby star clusters serve as anchors for the stellar models. Until now, we only had accurate distances to the much younger open clusters inside our galaxy because they are closer to Earth."

By contrast, about 150 globular clusters orbit outside of our galaxy's comparatively younger starry disk. These spherical, densely packed swarms of hundreds of thousands of stars are the first homesteaders of the Milky Way.

The Hubble astronomers used trigonometric parallax to nail down the cluster's distance. This technique measures the tiny, apparent shift of an object's position due to a change in an observer's point of view. Hubble measured the apparent tiny wobble of the cluster stars due to Earth's motion around the Sun.

To obtain the precise distance to NGC 6397, Brown's team employed a clever method developed by astronomers Adam Riess, a Nobel laureate, and Stefano Casertano of the STScI and Johns Hopkins University, also in Baltimore, to accurately measure distances to pulsating stars called Cepheid variables. These pulsating stars serve as reliable distance markers for astronomers to calculate an accurate expansion rate of the universe.

With this technique, called "spatial scanning," Hubble's Wide Field Camera 3 gauged the parallax of 40 NGC 6397 cluster stars, making measurements every 6 months for 2 years. The researchers then combined the results to obtain the precise distance measurement. "Because we are looking at a bunch of stars, we can get a better measurement than simply looking at individual Cepheid variable stars," team member Casertano said.

The tiny wobbles of these cluster stars were only 1/100th of a pixel on the telescope's camera, measured to a precision of 1/3000th of a pixel. This is the equivalent to measuring the size of an automobile tire on the moon to a precision of one inch.

The researchers say they could reach an accuracy of 1 percent if they combine the Hubble distance measurement of NGC 6397 with the upcoming results obtained from the European Space Agency's Gaia space observatory, which is measuring the positions and distances of stars with unprecedented precision. The data release for the second batch of stars in the survey is in late April. "Getting to 1 percent accuracy will nail this distance measurement forever," Brown said.
-end-
The team's results appeared in the March 20, 2018, issue of the Astrophysical Journal Letters.

The research team consists of T. Brown, S. Casertano, and D. Soderblom (STScI); J. Strader (MSU); A. Riess and J. Kalirai (STScI, JHU); D. VandenBerg (UVic); and R. Salinas (Gemini).

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.

NASA's Hubble Portal: http://www.nasa.gov/hubble

Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu

Tom Brown
Space Telescope Science Institute, Baltimore, Maryland
410-338-4902
tbrown@stsci.edu

NASA/Goddard Space Flight Center

Related Hubble Space Telescope Articles:

New way to weigh a white dwarf: Use Hubble Space Telescope
For the first time, astronomers have used a novel method to determine the mass of a type of star known as a 'white dwarf' -- the shrunken corpse of a dead star that used to be like our sun.
NASA's James Webb space telescope completes acoustic and vibration tests
At NASA's Goddard Space Flight Center in Greenbelt, Maryland the James Webb Space Telescope team completed the acoustic and vibration portions of environmental testing on the telescope.
Probing seven worlds with NASA's James Webb Space Telescope
With the discovery of seven earth-sized planets around the TRAPPIST-1 star 40 light years away, astronomers are looking to the upcoming James Webb Space Telescope to help us find out if any of these planets could possibly support life.
NASA restarts rigorous vibration testing on the James Webb Space Telescope
Testing on the James Webb Space Telescope successfully resumed last week at NASA's Goddard Space Flight Center, in Greenbelt, Md.
Robot would assemble modular telescope -- in space
A new concept in space telescope design uses a modular structure and an assembly robot to build an extremely large telescope in space, performing tasks in which astronaut fatigue would be a problem.
Science instruments of NASA's James Webb Space Telescope successfully installed
With surgical precision, two dozen engineers and technicians successfully installed the package of science instruments of the James Webb Space Telescope into the telescope structure.
James Webb Space Telescope's golden mirror unveiled
NASA engineers recently unveiled the giant golden mirror of NASA's James Webb Space Telescope as part of the integration and testing of the infrared telescope.
Earth-space telescope system produces hot surprise
Combining an orbiting radio telescope with telescopes on Earth made a system capable of the highest resolution of any observation ever made in astronomy.
NASA marks major milestones for the James Webb Space Telescope
NASA's James Webb Space Telescope just got a little closer to launch with the completion of cryogenic testing on its science cameras and spectrographs and the installation of the final flight mirrors.
NASA's James Webb Space Telescope secondary mirror installed
The sole secondary mirror that will fly aboard NASA's James Webb Space Telescope was installed onto the telescope at NASA's Goddard Space Flight Center in Greenbelt, Maryland, on March 3, 2016.

Related Hubble Space Telescope Reading:

The Hubble Cosmos: 25 Years of New Vistas in Space
by David H. Devorkin (Author), Robert W. Smith (Author), Robert P. Kirshner (Foreword)

To celebrate NASA’s Hubble Space Telescope and its 25 years of accomplishments, let The Hubble Cosmos fill your mind with big ideas, brilliant imagery, and a new understanding of the universe in which we live. Relive key moments in the monumental Hubble story, from launch through major new instrumentation to the promise of discoveries to come. With more than 150 photographs including Hubble All-Stars—the most famous of all the noteworthy images—The Hubble Cosmos shows how this telescope is revolutionizing our understanding of the universe. View Details


Hubble's Universe: Greatest Discoveries and Latest Images
by Terence Dickinson (Author)

Praise for the first edition:
"Superbly well produced. Any engagement with this 'cosmic portfolio,' from picture gazing to deep reading, is grandly rewarded."
--Booklist

[starred review] "The book's precise descriptions and captions brilliantly complement the 300 full-color Hubble images . . . this is an amazing book . . . outstanding."
--Library Journal

"A treasure map to the majesty of our universe."
--Publishers Weekly

"A reminder that the finest telescope in space might also be the greatest camera ever... View Details


NASA Hubble Space Telescope - 1990 onwards (including all upgrades): An insight into the history, development, collaboration, construction and role of space telescope (Owners' Workshop Manual)
by David Baker (Author)

The Hubble Space Telescope is an international venture primarily between the USA and Europe. More than any other space project, Hubble has encouraged an expanding interest in popular astronomy. With stunning views of the cosmos, it has inspired a new generation of enthusiasts to study the night sky through simple telescopes or in books. As such it has linked space technology with popular interest in astronomy and has thrilled specialists and the lay public alike.

View Details


Hubble Space Telescope: Photographing the Universe (Xtreme Spacecraft)
by John Hamilton (Author)

Simple text and "out-of-this-world" photography introduce readers to NASA's Hubble Space Telescope, and its mission to photograph the wonders of the universe, far above the atmosphere of Earth. Important details covered include the space observatory's planning and engineering, its launch, its scientific discoveries, and how its images have changed our perception of the cosmos. Aligned to Common Core Standards and correlated to state standards. A&D Xtreme is an imprint of Abdo Publishing, a division of ABDO. View Details


Hubble Space Telescope 2019 12 x 12 Inch Monthly Square Wall Calendar by Wyman, Science Space Technology
by Inc. BrownTrout Publishers (Author), BrownTrout Publishers Editing Team (Editor), BrownTrout Publishers Design Team (Editor)

Hubble Space Telescope 2019 12 x 12 Inch Monthly Square Wall Calendar by Wyman, Science Space Technology View Details


Expanding Universe: Photographs from the Hubble Space Telescope
by Owen Edwards (Contributor), Zoltan Levay (Contributor)

Time, space, and a telescope: Hubble’s most magnificent images

With investigations into everything from black holes to exoplanets, the Hubble Telescope has changed not only the face of astronomy, but also our very sense of being in the universe. On the 25th anniversary of its launch into low-earth orbit, TASCHEN celebrates its most breathtaking deep space images both as scientific feats and as photographic masterpieces.

Ultra high-resolution and taken with almost no background... View Details


Hubble Space Telescope: New Views of the Universe
by Mark Voit (Author)

Colorful and awe-inspiring poster-size photographs of emerging star, nebulae, and other astronomical marvels highlight an exploration of the impact that the Hubble Space Telescope has had on scientific study and general appreciation of the wonders of the skies. Original. View Details


The Hubble Space Telescope (Space Tech)
by Blake Hoena (Author)

The Hubble Space Telescope is a lens for discovering the hidden secrets of outer space. The tool has zoomed in on unknown galaxies! This book gives young readers a close-up of the Hubble Space Telescope, showing off its mirrors, cameras, solar panels, and more.

View Details


The Hubble Space Telescope: From Concept to Success (Springer Praxis Books)
by David J. Shayler (Author), David M. Harland (Author)

The highly successful Hubble Space Telescope was meant to change our view and understanding of the universe. Within weeks of its launch in 1990, however, the space community was shocked to find out that the primary mirror of the telescope was flawed. It was only the skills of scientists and engineers on the ground and the daring talents of astronauts sent to service the telescope in December 1993 that saved the mission.

For over two decades NASA had developed the capabilities to service a payload in orbit. This involved numerous studies and the creation of a ground-based... View Details


Hubble: Imaging Space and Time
by David H. Devorkin (Author), Robert Smith (Author)

In the spirit of National Geographic’s top-selling Orbit, this large-format, full-color volume stands alone in revealing more than 200 of the most spectacular images from the Hubble Space Telescope during its lifetime, to the very eve of the 2008 final shuttle mission to the telescope. Written by two of the world’s foremost authorities on space history, Hubble: Imaging Space and Time illuminates the solar system’s workings, the expansion of the universe, the birth and death of stars, the formation of planetary nebulae, the dynamics of galaxies, and the mysterious force... View Details

Best Science Podcasts 2018

We have hand picked the best science podcasts for 2018. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Inspire To Action
What motivates us to take up a cause, follow a leader, or create change? This hour, TED speakers explore stories of inspirational leadership, and what makes some movements more successful than others. Guests include high school history teacher Diane Wolk-Rogers, writer and behavioral researcher Simon Sinek, 2016 Icelandic presidential candidate Halla Tómasdóttir, professor of leadership Jochen Menges, and writer and activist Naomi Klein.
Now Playing: Science for the People

#474 Appearance Matters
This week we talk about appearance, bodies, and body image. Why does what we look like affect our headspace so much? And how do we even begin to research a topic as personal and subjective as body image? To try and find out, we speak with some of the researchers at the Centre for Appearance Research (CAR) at the University of the West of England in Bristol. Psychology Professor Phillippa Diedrichs walks us through body image research, what we know so far, and how we know what we know. Professor of Appearance and Health Psychology Diana Harcourt talks about visible...