Sky & Telescope - August 2020 - 19

G REGG DINDER M A N / S&T

desert. ALMA uses 66 movable antennas to peer deep into
stars' natal clouds and other normally inaccessible locations.
Among its successes, the array is helping transform what we
know about planet formation (S&T: May 2020, p. 34).
Yielding an even larger distance between elements is the
Very Long Baseline Array (VLBA), its ten 25-meter radio
dishes spanning the U.S. from the Virgin Islands in the Caribbean to Hawai'i in the Paciﬁc. Astronomers record data with
these elements and ship them to Socorro, where a correlator
combines them into what one humongous telescope would
have seen. European scientists have forged another large
array, the European VLBI Network (EVN), with 22 antennas spread across Europe to places beyond, including Puerto
Rico, South Africa, and South Korea. And ﬁnally, the VLBA
and EVN can operate together - and voilà we have a radio
telescope with a diameter almost as big as Earth's.
But why conﬁne oneself to Earth? Wouldn't lobbing an
antenna into orbit provide that much longer a baseline? In
fact, there have already been several ambitious experiments
using space-based antennas, dating back to 1979 when the
Soviets shuttled a 10-meter telescope to Salyut 6. The ﬁrst
standalone orbiting radio telescope was Japan's 8-meter
antenna of the VLBI Space Observatory Program (VSOP),
which operated from 1997 to 2003. The latest in this line
was Russia's 10-meter Spektr-R, which operated from 2011 to
2019 and provided a baseline of around 350,000 km.
Building on these early space-based forays, radio astronomers hope to extend their reach even farther. The Event
Horizon Telescope (EHT) team, for example, is contemplating launching an antenna into Earth orbit or placing one on
the Moon. Those with big dreams are targeting the second
Lagrangian point, a location some 1.5 million km "behind"
Earth as viewed from the Sun where spacecraft can hover

with minimal effort. It boggles the mind to think of what a
virtual radio receiver of that size could reveal about supermassive black holes residing in distant galaxies.

Dial in to the Future
The EHT and ALMA technically work at frequencies beyond
the upper edge of what astronomers consider radio. Monster
arrays at lower frequencies are also currently in development.
The Square Kilometre Array (SKA), for example, will straddle
two continents, with antennas located in South Africa and
Western Australia. When completed it will include thousands
of antennas.
Astronomers also have plans to upgrade the VLA. The
Next-Generation VLA (ngVLA) will consist of 244 dishes each
18 meters in diameter, spread across a baseline more than
200 times longer than the current setup. The new network
will combine a tight spiral of dishes in the U.S. Southwest
with remote stations across the country.
We may well ask what radio telescopes in the making and
new technologies hold in store for us. What will we learn
about the formation of the ﬁrst stars and galaxies right after
the Big Bang? Or how planetary systems arise? Will we gain
insight into black holes . . . and ultimately understand gravity
better? From the magnetism that bathes the universe to the
growing number of distant cosmic ﬂashes called fast radio
bursts, the heavens are awash in mysteries that radio telescopes will help us solve. Stay tuned.

¢ After umpteen years of pointing X-ray and radio telescopes
at the universe, Observing Editor DIANA HANNIKAINEN has
switched to commanding backyard light buckets. She dedicates this article to the memory of Richard Hunstead (1943-
2020), her beloved mentor in radio astronomy.

p WORLDWIDE WEB OF DISHES The two largest VLBI networks are the U.S.-based VLBA (green) and the European VLBI Network (blue). Stations
participate in the network but also belong to other projects or organizations - for example, Arecibo Observatory in Puerto Rico is part of the European network but is operated by the U.S. National Science Foundation and the University of Central Florida.
sk yandtelescope.org * AUGUST 2 02 0

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Sky & Telescope - August 2020

Table of Contents for the Digital Edition of Sky & Telescope - August 2020