Optical and radio telescopes team up to spot transients

Shortly after its inauguration on 25 May, MeerLICHT , the new, €1 million robotic optical telescope located about 400 kilometers northeast of Cape Town, South Africa, will be synced up with the country’s 64-dish MeerKAT radio array. The unprecedented networking of optical and radio telescopes will enable astronomers to spot and scrutinize transients including supernovae, gamma-ray bursts, and a (so far) baffling class of energetic events called fast radio bursts.

Transients are a growing area of astrophysics study, with researchers employing algorithms to rapidly sift through sky survey images and pick out unexpected outbursts. But as their name suggests, transients can be very short-lived—in the case of fast radio bursts, milliseconds or less—which makes them very easy to miss and difficult to follow up on. By observing the same patch of sky at the same time at different wavelengths for a five-year period, MeerLICHT astronomers hope to get a better understanding of the physics and locations of transients. Analyzing fast radio bursts is a particular priority, since so far only radio telescopes have spotted the energetic outbursts in action.

“Studying the time-variable universe is the next big frontier in astronomy,” says David Buckley, an astronomer at the South African Astronomical Observatory, a partner in the MeerLICHT project.

Although astronomers have simultaneously observed the sky in the optical and radio range, those surveys usually last only hours or days, and they rarely have complete field-of-view overlap, says Robert Braun, science director of the organization building the Square Kilometre Array radio observatory. “Very few telescope-time allocation committees are comfortable granting highly oversubscribed observing time simply based on the hope that something interesting and unexpected might occur,” he says.

Built through an international collaboration of the Netherlands, UK, and South Africa, MeerLICHT is designed to look at whatever it is MeerKAT is observing. The optical telescope’s nearly 3-square-degree field of view was specifically chosen to match MeerKAT’s, says Patrick Woudt, an astronomer at the University of Cape Town and a coprincipal investigator on the project.

Astronomers investigating fast radio bursts are particularly excited about the new optical–radio network. First detected in 2007, the bursts emit luminous millisecond-long pulses of radio light, and their origin is a mystery. Researchers have detected about 30 bursts , all via radio telescopes. One of the bursts, FRB121102, has erupted multiple times, allowing radio astronomers to home in on a location that coincides with that of a dwarf galaxy about 3 billion light-years from Earth (see Physics Today, March 2017, page 22 ).

With the combination of MeerLICHT and MeerKAT, astronomers should not have to hope for a recurring burst in order to find its home. “With the link to MeerLICHT, we will immediately be able to see if there is a galaxy here and get the redshifts for the galaxy,” Woudt says. “It builds a much more complete picture instantly.” Spotting bursts simultaneously in optical and radio will enable researchers to better estimate the events’ energy output and to narrow down theoretical models for their origin, says Jason Hessels , an astronomer at the Netherlands Institute for Radio Astronomy, a MeerLICHT partner institution.

The value of MeerLICHT and MeerKAT canvassing the electromagnetic spectrum isn’t limited to fast radio bursts. The network will also be able to monitor the evolution of supernovae as well as gamma-ray bursts similar to the one triggered by a neutron-star collision that gravitational-wave observatories and a host of electromagnetic telescopes monitored last year (see Physics Today, December 2017, page 19 ).

Ultimately, MeerKAT will be incorporated into the Square Kilometre Array, which, when complete, will be the largest telescope in the world. But for the next five years, it will serve as half of a potent transient-hunting team.