In 2003, Michio Kaku, writer for the science and technology magazine Wired, wrote: “Once confined to fantasy and science fiction, time travel is now simply an engineering problem.” Similarly, once confined to fantasy and science fiction, knowledge of distant galaxies and the origins of the Earth is now simply an engineering problem.
The Hubble Space Telescope is a 24,500-pound instrument that was placed into orbit around the Earth in April 1990. This telescope is the largest and most versatile used to date. Recent data obtained using this telescope has elucidated astronomers’ understanding of the universe and its formations.
Using the latest technology, the Hubble Space Telescope looked back in time about 13 billion years and took the deepest images of the universe ever recorded, revealing the farthest and youngest galaxies ever observed. Yale Professor of Astronomy Pieter van Dokkum and his team, including graduate student Tomer Tal, was part of the larger Hubble team responsible for the discovery and analysis of these galaxies.
Hubble’s most recent pictures were taken in a region called Hubble Ultra Deep Field (HUDF), an area of the sky containing approximately 10,000 galaxies. Since 2003, the Hubble telescope has been focused on this region and has imaged numerous galaxies formed less than one billion years after the Big Bang. These images have allowed astronomers to determine the distribution, size, and luminosity of galaxies in different time periods—research essential to studying the evolution of galaxies. In particular, the most recent galaxies found by Hubble were formed only 600 million years after the Big Bang and are instrumental in supporting the current theory of galaxy formation.
Out of this World
First launched in April 1990, the telescope has sent thousands of space images back to eager researchers on Earth. The Hubble Space Telescope was developed to overcome a major problem with ground-based astronomy: the atmosphere.
In the atmosphere, air molecules are constantly in motion, so Earth based pictures of space are slightly blurred. Furthermore, the atmosphere blocks wavelengths of high-energy radiation such as X-rays, gamma rays, and some ultraviolet rays, making it impossible to get a complete image of space. The best way to overcome the difficulties caused by Earth’s protective atmosphere and obtain optimal space images is to place a telescope outside the atmosphere—literally out of this world. The Hubble Space Telescope is in low-earth orbit, 569 kilometers from Earth’s surface. There, the telescope can take pictures of the universe with resolution about ten times greater than telescopes on Earth.
Due to its high-resolution image capability, Hubble can take pictures of galaxies extremely far away and has helped astronomers discover the age of the universe (about fourteen billion years) and determine the movement and formation of galaxies. For example, since the universe is expanding and the speed of light is constant, researchers can see galaxies formed thirteen billion years ago in the state that they existed thirteen billion light-years ago.
In order to obtain images of galaxies more than thirteen billion light years away, Hubble employs the latest astronomical technology. Wide Field Camera 3 (WFC3) is a recently installed instrument that can detect ultraviolet, visible, and infrared radiation and is thus much more powerful than previous instruments that were sensitive only to visible light. While the extremely long exposure time is critical in obtaining images of far-away galaxies, the ability of WFC3 to pick up infrared radiation is even more essential. Due to the expanding universe, objects at a greater distance move away more quickly and, due to the Doppler effect, the light emissions shift towards the red end of the electromagnetic spectrum—a phenomenon known as redshift. When observing objects very far away, the redshift is so substantial that visible light shifts into the infrared spectrum and can only be detected by the new WFC3 instrument.
Hubble sends the emission spectra back to astronomers on Earth who analyze the data to try to determine how and when the galaxies were formed. Researchers can determine the relative age of a galaxy from these spectra. More specifically, older stars tend to peak on the red end of the spectrum, while newer stars are towards the blue end. Therefore, by using Hubble to image the same region of the universe with many different filters, scientists can approximate the era in which the galaxy was formed and obtain evidence about the evolution of galaxies in our universe.
In the Beginning: What Hubble Saw
In addition to providing backyard astronomers and space enthusiasts fascinating images of deep space, the Hubble Telescope has been instrumental in determining how galaxies formed after the Big Bang and how they move in space.
In Hubble’s early days of operation, researchers discovered that as they looked deeper into space, galaxies moved faster away from them. The galaxies were not actually moving farther away from the researchers, however; rather, the entire fabric of the universe was expanding. As an analogy, the universe can be compared to a loaf of raisin bread in the oven: as the bread rises, the entire volume of dough expands and, due to this expansion, the raisins all move apart from one another. Just as observed in space, the raisins on the outer edge of the loaf, which is analogous to galaxies farther away, move apart at the greatest rate.
The Big Bang theory of universe formation can be used to explain the expansion of the universe. According to this theory, the universe was extremely hot and dense about fourteen billion years ago. Since then, the universe has been rapidly expanding. Over extended periods of time, small bits of matter have gravitationally attracted other particles of matter to form denser regions that became stars and galaxies.
The Hubble Telescope was used to support this theory of universe expansion in 1993 when scientists wanted to learn more about specific galaxies at various distances from Earth. By using Hubble to image galaxies with various filters for different wavelengths of light, astronomers have been able to determine the approximate redshift of the farthest galaxies ever found.
These galaxies, formed only 600 million years after the Big Bang, appear at the blue end of the visible light spectrum and are very compact. The blue emission spectra indicate high frequency emissions, implying that the stars in the galaxies are very young—or that they were young thirteen billion years ago.
A Hierarchal Universe
In the 1980s, the leading theory of galaxy formation claimed that all galaxies began as massive clouds of gas that eventually collapsed into the dense galaxies observed today. More recently, however, a different theory of galaxy evolution has evolved. Called the “hierarchical theory of galaxy formation,” this theory states that galaxy formation is an active process: galaxies start small but grow in mass and size over time. The data analyzed by Van Dokkum and his team further demonstrates that massive galaxies have grown from the inside out and have built up density around a compact core. Therefore, Van Dokkum’s work is influential in that it supports the aforementioned hierarchical theory of galaxy formation.
Van Dokkum and his team studied the growth of massive galaxies, focusing on galaxies since z = 2. In astronomy, z is a dimensionless number indicating the redshift of the galaxy. A negative z value indicates blue-shifted galaxies, while a positive z value indicates that a galaxy is moving away from the observer, and thus is shifted to the red side of the spectrum. The team of astronomers showed galaxy density has nearly doubled since z = 2 (from z = 2 to z = 0). In other words, younger galaxies are substantially larger in mass than old galaxies. Van Dokkum and his team published their findings in a paper called “The Growth of Massive Galaxies Since z = 2” in February 2010.
Therefore, although seemingly simple and insignificant, the fact that the earliest galaxies were both compact and blue has important implications in determining the correct theory of galaxy formation. Hubble’s images indicate that young galaxies are very small and compact, thus supporting the hierarchical theory of formation. According to Tomer Tal, the findings “show that, in the early universe, you don’t really observe huge massive galaxies, [thus demonstrating that galaxies must] grow in size and mass over time.”
Looking Ahead: Retirement, Brainstorming, and Rebirth
In 2010, astronomers across the world were delighted with Hubble’s latest images. The work, however, isn’t over. The telescope has done its job but people will now spend years analyzing the data and trying to prove a variety of different theories. According to Tal, “you can take the same data sets and re-analyze them in different ways…there is so much information in each of those observations that one group of people cannot get everything out of it.” Therefore, while initial analysis was used to support a theory of galaxy formation, the same data can be used to develop and support other theories about the nature of the universe.
Furthermore, astronomers are always looking for more. They have images of the furthest known galaxies, but can they see even older galaxies? The most recent WFC3 addition has pushed the limits of astronomy but researchers are already looking into new ways to see into our universe’s past.
The renowned Hubble Space Telescope has grown old and is in disrepair; unfortunately, it is now too costly to maintain. Thus, it will be left to wither over the next few years. As Hubble transitions to retirement, the James Webb Space Telescope (JWST) is being developed and built. Larger than Hubble, the JWST will be even more sensitive and able to detect even more light photons. Scientists are hoping that this new telescope will be able to detect galaxies formed almost immediately after the Big Bang.
Why You Should Care
Galaxy formation is a fascinating subject filled with mystery, calculations, and beautiful pictures. Cosmology in general, however, has no immediate application to humans or life on Earth. So why do people care so much about proving one theory of galaxy evolution over another and developing the most high-tech devices?
In Tal’s opinion, “I think we’re just a curious species. We like to know. In general, with scientific research, a lot of it is done because we want to know and we want to expand our knowledge rather than we’re looking for applications.”
Within the field of astronomy, Hubble’s most recent findings are important in quenching the curiosity of our species and putting together the pieces of the mystery of the universe. In order to understand the formation of the universe and how the universe works, it is essential to understand both the big and small pictures: galaxies can be looked at as whole entities in the expanding universe or they can be broken down into smaller components, such as stars and planets. Either way, every bit of information collected brings mankind one-step closer to understanding its role in a seemingly infinite universe.
About the Author
Shirlee Wohl is a freshman in Calhoun College. She plans on majoring in Molecular Biophysics & Biochemistry, yet has always been fascinated by stars, the sky, and the seemingly infinite expansion of the universe.
Acknowledgements
The author would like to thank Tomer Tal for his help in understanding Hubble’s latest findings and their implications and for sharing his enthusiasm in astronomy.
Further Reading
The official Hubble Space Telescope Website: https://hubblesite.org/