60 inch telescope



** Synopsis: A blast of gamma rays from space detected in June 2016 is helping astronomers resolve long-standing questions about the universe’s most powerful explosions. **

In June 2016, an international team of 31 astronomers, led by the University of Maryland’s Eleanora Troja and including Arizona State University’s Nathaniel Butler, caught a massive star as it died in a titanic explosion deep in space.

The blast of the dying star released in about 40 seconds as much energy as the Sun releases over its entire lifetime, all focused into a tight beam of gamma rays aimed by chance toward Earth.

The team’s findings, reported in the scientific journal Nature, provide strong evidence for one of two competing models for how gamma-ray bursters (GRBs) produce their energy.

“These are the brightest explosions in the universe,” says Butler, an associate professor in ASU’s School of Earth and Space Exploration. “And we were able to measure this one’s development and decay almost from the initial blast.”

Quick reflexes

The gamma-ray blast on June 25, 2016, was detected by two NASA satellites that monitor the sky for such events, the Fermi Gamma-ray Space Telescope and the Swift Gamma-Ray Burst Mission.

The satellite observatories detected the burst of gamma rays, identified where in the sky it came from, and sent its celestial position within seconds to automated telescopes on the ground.

The MASTER-IRC telescope at the Teide Observatory in the Canary Islands observed it first, within a minute of the satellite notification. The telescope is part of Russia’s MASTER network of robotic telescopes at the Teide Observatory. It made optical light observations while the initial phase was still active, gathering data on the amount of polarized optical light relative to the total light produced.

After the Sun set over this facility eight and a half hours later, the RATIR camera in which ASU is involved began observing. RATIR stands for Reionization And Transients InfraRed camera; it is mounted on a 1.5-meter (60-inch) robotically controlled telescope located on San Pedro Mártir Peak, at Mexico’s National Astronomical Observatory in Baja California. Butler is the principal investigator for the fully-automated camera.

Butler explains, “At best, it takes a minute or two for our telescope to slew to the burst’s position. In this case, we had to wait for it to rise over the horizon. This means the gamma-ray burst itself had ended, and we were observing what’s called the afterglow. This is the fading explosion as the radiation shocks up the interstellar medium around the star that exploded.”

He says, “The RATIR camera lets us take simultaneous images in six colors, two optical and four near-infrared. Over the past five years, RATIR has imaged 155 gamma-ray bursts.”

Mystery beams of energy

While gamma-ray bursters have been known for about fifty years, astronomers are still mostly in the dark about how they erupt.

“Despite a long history of observations,” Butler says, “the emission mechanism driving gamma-ray bursters remains largely mysterious.”

Gamma-ray bursts are detected approximately once per day and are brief, but intense, flashes of gamma radiation. They come from all different directions in the sky, and they last from tens of milliseconds to about a minute, making it hard to observe them in detail.

Astronomers believe most of these explosions are associated with supernovas. These occur when a massive star reaches the end of its normal existence and blows up in a colossal explosion. A supernova throws off some of the star’s outer layers, while its core and remaining layers collapse in a few seconds into a neutron star or, in the case of highly massive stars, a black hole.

Continued RATIR observations over weeks following the June 2016 outburst showed that the gamma rays were shot out in a beam about two degrees wide, or roughly four times the apparent size of the Moon. It was sheer chance that Earth happened to lie within the beam.

Beaming effects, Butler says, may result from the spin of the black hole produced after the supernova explosion, as it releases material along its poles.

Magnetic focus

“We think the gamma-ray emission is due to highly energetic electrons, propelled outward like a fireball,” Butler says. Magnetic fields must also be present, he adds, and theories differ as to how the fields are produced and to what extent the flow of magnetic energy outward is important.

A key diagnostic is measuring the radiation’s polarization, he explains. This, astronomers think, is largely controlled by the strength of the magnetic fields that focus the radiation. Butler says, "Measuring the strength of magnetic fields by their polarization effects can tell us about the mechanisms that accelerate particles such as electrons up to very high energies and cause them to radiate at gamma-ray energies.”

In the case of the June 2016 blast, the scientists were able to measure polarization using MASTER within minutes, an unprecedented early discovery. The large amount of polarization the team observed indicates that powerful magnetic fields were confining and directing it. This lends support for the magnetic origin model for gamma-ray bursters.

While gamma-ray bursters have many more mysteries to be unfolded, Butler says, “this is the first strong evidence that the early shocks generated by these bursts are magnetically driven.”

Astronomers discover 'heavy metal' supernova rocking out

Many rock stars don’t like to play by the rules, and a cosmic one is no exception. A team of astronomers has discovered that an extraordinarily bright supernova occurred in a surprising location. This “heavy metal” supernova discovery challenges current ideas of how and where such super-charged supernovas occur.

Supernovas are some of the most energetic events in the Universe. When a massive star runs out of fuel, it can collapse onto itself and create a spectacular explosion that briefly outshines an entire galaxy, dispersing vital elements into space.

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Photo: Mount Wilson Observatory, 60-inch telescope, lithograph printed on medium thin matte finish paper from encyclopedia printed, USA in 1959.

Three fine normal spirals viewed almost edge on, Top: NGC 4594 in Sextans, 1914. Centre: NGC 5746 in Virgo, 1914 Bottom: NGC 4565 in Coma Berenices, 1910.  Note the progressive development of the arms at the expense of the nucleus.


The Griffith Observatory.

On my recent trip to LA I had time to visit the Griffith Observatory and was absolutely moved by it’s history.

Griffith J. Griffith was introduced to astronomy through the Astronomical Section of the Southern California Academy of Sciences. He was also impressed by his visits to the new research observatory established at Mount Wilson in 1904. He believed that an individual gained an enlightened perspective when looking at the skies. His reaction after looking through the 60-inch telescope at Mount Wilson – then the largest in the world – was described by John Anson Ford: “The experience moved him profoundly - a distant, heavenly body suddenly being brought so close and made so real!” Ford quotes Griffith as saying: 

“Man’s sense of values ought to be revised. If all mankind could look through that telescope, it would change the world!”

Griffith’s experience on Mount Wilson focused his desire to make science more accessible to the public. On December 12, 1912, he offered the City of Los Angeles $100,000 for an observatory to be built on the top of Mount Hollywood to be fully owned and operated by the City of Los Angeles. Griffith’s plan for the observatory would include an astronomical telescope open to free viewing, a Hall of Science designed to bring the public into contact with exhibits about the physical sciences, and a motion picture theater which would show educational films about science and other subjects.