Astronomers Discover Star With the Shortest Orbital Period Around Milky Way Galaxy’s Central Black Hole (October 4, 2012)

TORONTO, ON (Tuesday, 2 October 2012) – A team from UCLA that includes an astronomer with the Dunlap Institute, University of Toronto, has discovered a star that orbits the supermassive black hole at the centre of the Milky Way Galaxy in less time than any other known star.

Referred to as S0-102, the star circuits our galaxy’s centre in 11.5 years, or less time than Jupiter takes to orbit the Sun. According to the Dunlap’s Tuan Do, “Because of its proximity to the central black hole, S0-102 gives us an excellent opportunity to test Einstein’s General Relativity.”

The team’s findings will be published in the journal Science on Friday, 5 October 2012. They are the latest results from the 17-year effort of the UCLA Galactic Center Group, led by Prof. Andrea Ghez of the Department of Physics & Astronomy.

It was by studying the stars in the Milky Way Galaxy’s central region that Ghez and her team originally discovered the supermassive black hole in the heart of our galaxy. Known as Sgr A* (Sagittarius A-star), the prodigious object contains the mass of four million stars equal in mass to our Sun. “Having proved that black holes exist,” says Ghez, “our research today aims to understand their nature and how they warp space and time.”

There are thousands of stars within a few light-years of our galaxy’s centre. As Do, a co-author on the Science paper, describes it, “This region is the most extreme environment in the galaxy. It has the highest density of stars—equivalent to having over a million stars between the Sun and our next closest star, Alpha Centauri. The stars closest to Sgr A* are travelling at over 4000 kilometres per second. That’s 1% the speed of light.”

The previous stellar record holder for orbiting Sgr A* was a star called S0-2 with a galactic orbital period of 16 years. According to General Relativity, the elliptical orbits of objects like S0-2 and S0-102 should themselves “rotate”, creating a rosette-pattern over time. This motion is known as precession and is most easily observed in bodies orbiting close to massive objects.

But the mass of other stars near the galaxy’s centre creates a different type of precession which is hard to separate from precession caused by General Relativity. By studying the orbits of S0-02 and S0-102 together, the Galactic Center Group will be able to distinguish between the two precessions. And according to Ghez, “It is conceivable that we will be able to observe deviations from Einstein’s theory in regions where S0-102 and other short period stars reside.”

S0-102 was discovered using images taken with the twin 10-metre telescopes of the Keck Observatory on Mauna Kea in Hawai’i. These included observations with the Keck II telescope using adaptive optics and laser guide-star technology which corrects for distortions caused by the Earth’s atmosphere. With a resolution greater than that of the Hubble Space Telescope, the observations allow Ghez, Do and the group to resolve individual stars in the crowded region.

Do joined the Dunlap Institute for Astronomy & Astrophysics, University of Toronto, in August 2012, where he will continue to work with the UCLA group in preparation for observations of the galactic centre using the next generation Thirty Meter Telescope (TMT). Scheduled to begin operation later this decade, the TMT will not only substantially improve the measurements for S0-102; the group fully expects that it will also lead to the discovery of many, even shorter-period stars.

CONTACT INFORMATION:

Dr. Tuan Do
Dunlap Fellow
Dunlap Institute for Astronomy & Astrophysics
University of Toronto
e: do@dunlap.utoronto.ca
p: 416-78-2215
www.dunlap/utoronto.ca/dr-tuan-do
www.di.utoronto.ca/~do

Chris Sasaki
PIO, Communications and New Media Specialist
Dunlap Institute for Astronomy & Astrophysics
University of Toronto
e: csasaki@dunlap.utoronto.ca
p: 416-978-6613

Prof. Andrea Ghez
Principal Investigator
UCLA Galactic Center Group
Department of Physics & Astronomy
UCLA
e: ghez@astro.ucla.edu
p: 310-206-0420

About the Dunlap Institute for Astronomy & Astrophysics, University of Toronto: The Dunlap Institute was established in May 2008 at the University of Toronto, creating a dynamic centre for astronomical research along with the university’s Department of Astronomy & Astrophysics and Canadian Institute for Theoretical Astrophysics. The Dunlap Institute continues the legacy of the David Dunlap Observatory of developing innovative astronomical instrumentation, including instrumentation for the largest telescopes in the world. The research of its faculty and Dunlap Fellows spans the depths of the Universe, from the discovery of exoplanets around nearby stars, to star formation, black holes, dark matter, high-redshift galaxies, and the Big Bang. The institute also continues a strong commitment to developing the next generation of astronomers through education programs, and fostering public engagement in science through a wealth of outreach activities.

For more information about the Dunlap Institute: www.dunlap.utoronto.ca

A Grand Design Spiral Galaxy Before Its Time

TORONTO, ON (12 JULY 2012) – A team led by an astronomer at the Dunlap Institute for Astronomy & Astrophysics, University of Toronto, has discovered a spiral galaxy that appears to have formed a billion years before other spirals. The galaxy is 10.5 billion light-years from Earth, putting it at a time when the Universe was only three billion years old and spirals were extremely rare.

According to Dunlap Institute postdoctoral fellow and Principal Investigator David Law, “Seeing this galaxy amongst the irregular, young galaxies of that epoch is like seeing a fully-formed adult in a room of grade-school children.”

Law says, “The fact that this galaxy exists is astounding. Current wisdom holds that such grand-design spiral galaxies simply didn’t exist at such an early time in the history of the Universe.” Most galaxies in the three billion year old Universe are clumpy and irregularly-shaped; they haven’t formed the well-defined spiral arms we see in galaxies like the iconic M51 Whirlpool Galaxy.

The rest of Law’s team comprises researchers from UCLA, Caltech, UC Riverside, Steward Observatory, and UW Milwaukee. The Space Telescope Science Institute provided principal funding for the work, the results of which will be published in the 19 July 2012 issue of the science journal Nature.

The researchers noticed the galaxy, identified as BX442, in images they obtained using the Hubble Space Telescope (HST). Law’s co-investigator Alice Shapley, from UCLA, remembers coming across the galactic oddity. “Among the irregular and clumpy galaxies of the early Universe, this well-ordered spiral stuck out like a sore thumb—a beautiful and amazing sore thumb.”

But, while the Hubble image revealed the galaxy’s spiral structure, it didn’t prove conclusively that the galaxy rotated. In order to settle this question, Law and Shapley used the Keck II telescope in Hawaii to study the object’s internal motions. The twin Keck telescopes, each with 10-metre diameter primary mirrors, are the largest optical/infrared telescopes in the world. The Keck II is equipped with a laser-guide-star adaptive-optics system which corrects for the distortion of in-coming light caused by the Earth’s turbulent atmosphere, resulting in images as sharp as those taken with the HST.

Law and Shapley used an integral-field spectrograph called OSIRIS (OH-Suppressing Infrared Imaging Spectrograph) on the Keck II telescope to sample light from different parts of the galaxy. These samples showed that those parts were moving at different speeds relative to us—revealing that it is indeed a spiral disk, rotating roughly as fast as our own Milky Way Galaxy, but much thicker and forming stars more rapidly.

While the spiral structure and rotation have been confirmed, the reason for the spiral structure remains a mystery; it’s unclear why this galaxy has been able to form such sweeping spiral structures so much earlier than other galaxies. According to Shapley, “Immediately, we started wondering how such a spiral galaxy might form in the early universe.” One possibility, Law suggests, is the presence of a dwarf companion galaxy that they observe in the process of merging with the main galaxy. Just as Messier 51 is subject to tidal forces from a dwarf companion of its own, gravitational interaction with the newly-discovered galaxy’s dwarf companion might help excite transient spiral structure within the main galaxy. Understanding this mechanism in greater detail could help explain the formation and evolution of modern spirals like our own Milky Way Galaxy.

CONTACT INFORMATION:

Dr. David Law, Lead Author/Principal Investigator
Dunlap Fellow
Dunlap Institute for Astronomy & Astrophysics
University of Toronto
email: drlaw@dunlap.utoronto.ca
phone: 416-946-5435
www.dunlap.utoronto.ca/david-law/
www.di.utoronto.ca/~drlaw

Chris Sasaki
PIO, Communications and New Media Specialist
Dunlap Institute for Astronomy & Astrophysics
University of Toronto
email: csasaki@dunlap.utoronto.ca
phone: 416-978-6613

About the Dunlap Institute for Astronomy & Astrophysics, University of Toronto: The Dunlap Institute was established in May 2008 at the University of Toronto, creating a dynamic centre for astronomical research along with the university’s Department of Astronomy & Astrophysics and Canadian Institute for Theoretical Astrophysics. The Dunlap Institute continues the legacy of the David Dunlap Observatory of developing innovative observational techniques, instruments, telescopes and observatories—including instrumentation for the largest telescopes in the world. The research of its faculty and postdoctoral fellows spans the depths of the Universe, from the discovery of planets around nearby stars, to black holes, dark matter, and the study of galaxies at the beginning of time. The institute also continues a strong commitment to developing the next generation of astronomers through education programs, and passionately fostering public engagement in science through a wealth of outreach activities.