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Putting Einstein’s theory of general relativity to the test
A simulated image of the black hole Sagittarius A*. A circular shadow would prove general relativity is valid. More complicated shapes like an oval or heart would prove general relativity must be corrected within strong gravitational regimes.
by Victoria Van Cappellen. This article originally appeared on Waterloo Stories.
Waterloo astrophysicists are leading a team of researchers who have devised a new way to test Einstein’s theory of general relativity within Sagittarius A* - the supermassive black hole at the center of the Milky Way.
Tim Johannsen and Avery Broderick, along with international colleagues, will use the new method in gravitational conditions that are so extreme, the results will usher in a new era in gravitational research, validating – or disproving – general relativity in its most exotic manifestations.
“Based on the observations we expect to make this spring with the Event Horizon Telescope, we’ll be able to make incredibly precise statements about the nature of this black hole,” says Johannsen, also a post-doctoral fellow at the Perimeter Institute for Theoretical Physics.
The Event Horizon Telescope is a global array of radio telescope sites spanning the Earth, designed to image two supermassive black holes: Sagittarius A* and another located in the centre of the M87 galaxy. Images are captured not in visible light, but in the radio portion of the electromagnetic spectrum.
The researchers’ method, recently published in Physical Review Letters, proposes to compare predictions made by general relativity against this first-ever, live image of Sagittarius A*, a black hole four million times the mass of our own sun.
According to general relativity, a black hole such as Sagittarius A* should exhibit a nearly circular shadow based on just two properties – mass and spin. If the researchers find the shadow requires additional parameters, for example, if it is oval or heart-shaped, then general relativity must be incomplete.
“Just like general relativity is a small correction to Newtonian gravity in our solar system, we may also need such a correction to general relativity in a strong gravitational regime,” says Johannsen.
Preliminary findings using only three of eight Event Horizon Telescope sites support Einstein’s theory of general relativity. But when all eight sites come online this spring, the observations will be so sensitive and sharp that their conclusion will be almost absolute.
Avery Broderick is an associate professor in the Department of Physics and Astronomy at the University of Waterloo and a faculty member at the Perimeter Institute for Theoretical Physics.
SWEC launches equity e-newsletter
The Faculty Association of the University of Waterloo’s Status of Women & Equity Committee (SWEC) has launched the UWaterloo Equity Update, a biweekly newsletter featuring events and opportunities related to the committee's gender and equity mandate.
The first issue went out on Thursday, September 15.
One of the Faculty Association’s major initiatives is its Status of Women and Equity Committee (SWEC), which engages in educational and advocacy activities related to the status of women and with broader equity issues such as those arising from gender, ethnicity, race, sexual orientation, disability, religion, age, or gender identity.
The newsletter brings together a range of events and opportunities across campus and in the community related to the committee's equity mandate, from seminars and conferences to scholarships and grants.
Construction on and off campus and other notes
Plant Operations is reporting that on Wednesday September 28 and Thursday September 29, the road between the Tatham Centre and the School of Accountancy will be closed for paving and curb work at the theatre road.
Information Systems and Technology (IST) has made an announcement about the recently-brought-to-light Yahoo! data breach.
"Personal details of Yahoo! account holders, including password hashes, were leaked. Yahoo! reports approximately a half-billion accounts affected," says the announcement from IST. "Since there are members of the University of Waterloo community who forward their email to Yahoo! accounts, IST strongly recommends that those affected change their Yahoo! passwords as soon as possible."
This breach affects Yahoo! users who created their accounts before 2015, and who have not changed those passwords since.
"Any person who has created a Yahoo! account before 2015 should change that account password as soon as possible," says IST. "Those who use Yahoo! for email should be especially prudent in changing their Yahoo! password since email accounts are often central to the password reset workflow for other websites. Similarly, those who reuse the same password at other websites should change the password at those sites as well. To change your WatIAM password visit the WatIAM website."
IST reminds us that it is recommended that users use a different password for each service that requires a login.
Anyone with questions or concerns should contact the IST Service Desk at helpdesk@uwaterloo.ca, ext. 44357 or the IST– Security Operations Centre at soc@uwaterloo.ca, ext. 41125.
It's about that time for another round of TheGROOVE dance classes with Cindy, beginning next week on campus. The classes take place Tuesdays from 5:00 p.m. to 6:00 p.m. and on Wednesdays from 12:00 p.m. to 1:00 p.m. in CPH 4333. To get more information about pricing and to register, contact Cindy Howe by sending an email to cindy@uwaterloo.ca.
The Federation of Students is encouraging undergraduates to make their voice heard. All undergraduates at the University of Waterloo will be able to cast a ballot for the WPIRG fee referendum on vote.feds.ca from 10:00 a.m. on Monday, September 26 until 10:00 p.m. on Wednesday, September 28. More information about the referendum is available online.