March 14th, 2021
During its 31 years of activity, the Hubble Space Telescope has been “one of the most successful scientific experiments in history,” used to research numerous fields of astronomy ranging from cosmology and the expansion of the universe to the characterization of exoplanets, said astronomer Tom Brown of the Space Telescope Science Institute in a March 2 online presentation.
A joint NASA/European Space Agency project, Hubble launched in 1990. Through servicing missions conducted between then and 2009, it became increasingly more powerful.
The telescope orbits the Earth at an altitude of 333 miles (536 kilometers) and takes 95 minutes to circle the planet. It is powered by solar arrays when traversing Earth’s day side and batteries when passing over its night side.
Science instruments currently operating on Hubble include the Cosmic Origins Spectrograph, which conducts faint ultraviolet spectroscopy; the Space Telescope Imaging Spectrograph, which conducts spectroscopy and imaging in both optical and ultraviolet light; the Advanced Camera for Surveys (ACS), which conducts wide-field imaging and slitless spectroscopy; the Wide Field Camera 3 (WFC3), which also conducts wide-field imaging and slitless spectroscopy as well as astrometry; and the Fine Guidance Sensors, which conduct astrometry and serve as the pointing control system.
Hubble’s strength is that it conducts a combination of powerful imaging and spectroscopy, Brown said. Its ultraviolet imaging capability is especially crucial because ultraviolet light cannot be imaged from the ground.
Spectroscopy, which disperses light from its sources into its component colors, “informs astrophysical research regarding temperature and chemistry.”
Hubble was used to both image the massive star Eta Carinae, showing its structure, and take a spectrum of it, which revealed its chemical makeup.
ACS and WFC3 are significantly more powerful than previous generations of instruments on Hubble, Brown emphasized.
Hubble has imaged numerous nearby galaxies, many of them spirals, as well as much more distant galaxies. “Now, when we get an image with Hubble, we get not only the object we’re looking at, but we tend to get much of the universe behind that object for free in the same exposure.” This was not possible with earlier generations of Hubble cameras, Brown said.
Science done by Hubble includes the study of galaxies, the intergalactic medium and circumgalactic medium, large scale structure, the solar system, stellar physics, stellar populations, supermassive black holes, and exoplanets and planet formation.
Approximately 1,000 peer-reviewed papers based on Hubble data are published every year. These include papers by scientists who go back into Hubble archives and do new science using that data.
Observing time on Hubble is awarded through a dual anonymous peer review system to avoid bias, Brown said. Demand for time on the telescope exceeds time available on it by more than five to one.
The two phenomena most studied with Hubble are cosmic expansion and exoplanet science, he said.
Much science can be done through enhanced gravitational lensing, which allows astronomers to see extremely distant objects, including galaxies 10 times fainter than would otherwise be observable.
Measuring cosmic expansion, or the expansion of the universe, was a priority from the time the telescope launched. Scientists at the time hoped to use Hubble to characterize the rate at which the universe is expanding.
What was not known at that time but discovered through subsequent observations of supernovae, is that expansion of the universe goes through periods of both deceleration and acceleration.
“We are now in an era of precision cosmology where people are measuring the expansion of the universe rate using different methods. Those methods don’t always give the same answer, which might be implying new physics,” Brown said.
Exoplanet study now makes up 20% of Hubble’s observing time. But when Hubble launched, exoplanets had not yet been discovered.
While Hubble is not the main facility for discovering exoplanets, it is the main one for studying their atmospheres, used for follow up observations once other facilities find the planets.
Hubble measures the variation of light that occurs as an orbiting planet passes in front of its host star.
The oldest known exoplanet was found orbiting a pulsar in 1992. Three years later, scientists discovered the first exoplanet orbiting a normal star. Today, thousands of exoplanets have been and continue to be discovered.
A technique known as spatial scanning, developed over the past decade, involves intentionally dragging the telescope across a field of view. This enables scientists to obtain high-precision parallaxes and astrometry and get hundreds of measurements of stars’ positions.
Hubble also is used in conjunction with NASA and ESA missions. Scientists on the New Horizons mission to Pluto used it to navigate a path for the spacecraft safe from debris, discovered four small moons orbiting Pluto, and identified a second flyby target, the Kuiper Belt Object Arrokoth.
To assist the Juno mission to Jupiter, scientists have been observing the giant planet with Hubble at the same time Juno is doing so up close while researchers are also looking at the gas giant with the ground-based Gemini Observatory in Hawaii.
Researchers are using Hubble to study the nature of black holes and the disks of material falling into them, as well as to learn more about gravitational waves, which are ripples in the fabric of space-time produced by the mergers of two massive objects, such as neutron stars or black holes.
When it was last serviced in 2009, scientists hoped Hubble would last until 2016. Having outlasted those expectations, it is now anticipated to play a major role in the study of astrophysics over the next decade.
Together with the James Webb Space Telescope, scheduled for launch later this year, Hubble will further probe cosmic expansion and dark energy, provide new insights into exoplanets and their atmospheres, cooperate with solar system exploration missions, and assist scientists in understanding discoveries made by other facilities.
Video courtesy of the Space Telescope Science Institute
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.
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