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Tag Archives: Einstein

The detection of gravitational waves by the Laser Interferometer Gravitational-wave Observatory (LIGO) opens up a method of observing the universe in a new way, perhaps comparable to the advance that Galileo made in 1609 by turning a telescope on the heavens.

Many awards have been given to Kip Thorne of Caltech, who worked out the theory decades ago, and the people who built LIGO over 40 years until its success in 2015.  The 2017 Nobel Prize in Physics was awarded to Prof. Thorne as well as Barry Barish and Rainer Weiss, half to Weiss for beginning the actual method of the successful observations and one quarter each to the other two.

2017PhysicsNobel

Credit: Niklas Elmehed/The Nobel Prize Foundation

 

The October 3, 2017, award of the Nobel Prize was much anticipated and is well deserved.  See, for example, coverage in the following media:
Physics Today
NY Times
Nature
Science
The Atlantic provides a thoughtful reflection on the merits of the Nobel prize.

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An update for Section 13.3f (pp. 352-355) in Pasachoff & Filippenko, The Cosmos, 4th ed:
In what many think is the most important step in astronomy since Galileo first turned a telescope on the heavens in 1609, ripples in space-time known as gravitational waves were detected on September 14, 2015, and reported to the world at large on February 11, 2016. Scientists gathered all over in auditoriums at the National Press Club in Washington, at Caltech, at MIT, in Moscow, and in many other places for the epochal event. “Ladies and gentlemen, we have detected gravitational waves,” said the executive director of the LIGO Laboratory. “We did it!”

The observational existence of gravitational radiation had been established by the changing period of the Hulse-Taylor “double pulsar” at a rate that matched the energy loss expected from the emission of gravitational waves (Section 13.3f, pp. 352-354), but the gravitational waves themselves – distortions of space-time – had not been detected directly until the Advanced LIGO (Laser Interferometer Gravitational Wave Detector) picked up a signal in its engineering run on September 14, 2015.  The signal, which could be heard as an upwards “chirp” in the audio range, resulted from two black holes 1.3 billion light years away, each containing about 30 solar masses, spiraling rapidly into each other and merging to become a single black hole with almost the same total mass but with 3 solar masses of material converted into energy in the form of gravitational waves.

Advanced LIGO has about 3 times the sensitivity of the earlier LIGO, and this event was within that advance of sensitivity. A further gain of 3x is expected with Advanced LIGO in the future.

Scientific papers were published February 11, 2016, in the Physical Review Letters and in the Astrophysical Journal Letters.

A few days later, I [JMP] attended a two-hour evening session at Caltech’s main auditorium to hear the principals of the LIGO project speaking, and I had the feeling that it was just like being at a meeting of the Lincei Academy in Florence in 1610 to hear Galileo speak about his new discoveries with the [optical] telescope.

There are many links to discussions and animations available. Here are some of them:

Popular and academic press:
New York Times coverage (includes movie); also NYT Opinion piece and an NYT Editorial a few days later, justifying scientific inquiry; a congressman’s letter, and sound bites from scientists.
Nature coverage (with explanatory graphics)
Science magazine in depth (requires subscription to access full text)
New Yorker article (with an account of LIGO’s inception and development)
Physics Today comparison of gravitational waves and sound waves
The Wall Street Journal and Michio Kaku’s desciption.

Societies and organizations:
American Physical Society Viewpoint
The Kavli Foundation Scientific spotlight
Caltech (press releasesillustrations, movies and animations)
NSF press release
AAPT resources on gravitational waves
STFC (UK) press release
Cornell Chronicle and media statement
University of Texas Rio Grande Valley press release
ESA congratulations
CSIRO (Australia) news release

LIGO websites:
LIGO labs (Observatories: Livingston | Hanford); Advanced LIGO; LIGO Scientific Collaboration; LIGO Partner Experiments and Collaborations

 

 

 

 

 

The European Research Council (ERC) has awarded 14 million euros (around $19 million) to a team of European astrophysicists to construct the first accurate image of a black hole. The team will test the predictions of current theories of gravity, including Einstein’s general theory of relativity. The funding is provided in the form of a synergy grant, the largest and most competitive type of grant of the ERC. This is the first time an astrophysics proposal has been awarded such a grant.

The team, led by investigators at the University of Nijmegen, the Max Planck Institute for Radio Astronomy, and Goethe University in Frankfurt, hopes to measure the shadow cast by the event horizon of the black hole in the center of the Milky Way, find new radio pulsars near this black hole, and combine these measurements with advanced computer simulations of the behavior of light and matter around black holes as predicted by theories of gravity. They will combine several telescopes around the globe to peer into the heart of our own galaxy, which hosts a mysterious radio source called Sagittarius A* which is considered to be the central supermassive black hole. (See p. 383 and Section 15.5, p. 391.)

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Credit and © M. Moscibrodzka & H. Falcke, Radboud-Universität Nijmegen

Black holes are notoriously elusive with a gravitational field so large that even light cannot escape their grip. The team plans to make an image of the event horizon – the border around a black hole which light can enter, but not leave.  The scientists want to peer into the heart of our own galaxy, which hosts a mysterious radio source called Sagittarius A*. The object is known to have a mass of around 4 million times the mass of the Sun and is considered to be the central supermassive black hole of the Milky Way.

As gaseous matter is attracted towards the event horizon by the black hole’s gravitational attraction, strong radio emission is produced before the gas disappears. The event horizon should then cast a dark shadow on that bright emission. Given the huge distance to the center of the Milky Way, the shadow is equivalent to the size of an apple on the Moon seen from Earth. By combining high-frequency radio telescopes around the world, in a technique called very long baseline interferometry (VLBI), even such a tiny feature is, in principle, detectable.

In addition, the group wants to use the same radio telescopes to find and measure pulsars around the very same black hole. Pulsars are rapidly spinning neutron stars, which can be used as highly accurate natural clocks in space. While radio pulsars are found throughout the Milky Way, surprisingly none had been found in the center of the Milky Way until very recently.