Sky & Telescope - USA (2019-08)

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SPECTRUM by Peter Tyson

A Feast for the Eyes

FORTUNATELY FOR ASTRONOMY, light comes in many fl avors. If

we could observe celestial objects and events only in the visible

light our eyes can perceive, we’d miss so much of what is on offer

out there. It would be like tasting only sweet foods but not salty,

bitter, sour, or savory. How limited our palate would be!

But what our eyes can’t picture, our instruments can. They can capture and

focus low-energy radio, microwave, and infrared photons as well as high-energy

ones such as ultraviolet, X-rays, and gamma rays. Through our ingenuity, light

from the entire electromagnetic spectrum has become viewable to us.

X-ray astronomy, for one, has come leaps and bounds since its start in the

early 1960s, as News Editor Monica Young details in our cover story on page 14.

One striking measure of this is that, between the launch of the fi rst focusing

X-ray telescope aboard a sounding rocket in 1965, and the launch of the Chan-

dra X-ray Observatory in 1999, the sensitivity of

X-ray telescopes improved 100 million times.

X-rays are emitted when matter has been heated

to temperatures in the millions of degrees, or

when particles have been accelerated to relativistic

speeds. By allowing us to “see” this high-energy

light, X-ray space telescopes like NASA’s Chandra

and the European Space Agency’s XMM-Newton —

both 20 years old this year — enable us to witness

events and objects in some of the universe’s most

extreme environments.

We can discern, for example, multi-million-

degree gas strands around ultra-dense neutron

stars or stellar black holes, whose wickedly strong gravity has yanked the gas

from a companion star. We can see the crescent-shaped shock front from a

supernova, where the force from what was an unimaginably violent explosion

has compressed interstellar gas so quickly as to leave it glowing in X-ray light.

X-ray astronomy helps us address fundamental questions. One example

involves the superhot gas that permeates galaxy clusters, the largest structures

in the universe. Studying these nebulous forms aids astronomers in tackling

what Riccardo Giacconi, the father of X-ray astronomy who died in December,

called “one of the most interesting open questions of modern cosmology” —

namely, how structure developed and evolved in the early universe.

X-rays can shoot right across the cosmos, yet Earth’s atmosphere absorbs

them. Imagine: After traveling for millions of years, they’re

stopped at the last nanosecond! But we get around that

barrier with X-ray space telescopes, which spread out a

celestial smorgasbord for our delectation and investigation.

Editor in Chief

The Essential Guide to Astronomy

Founded in 1941 by Charles A. Federer, Jr.

and Helen Spence Federer

EDITORIAL

Editor in Chief Peter Tyson

Senior Editors J. Kelly Beatty, Alan M. MacRobert

Science Editor Camille M. Carlisle

News Editor Monica Young

Associate Editors S. N. Johnson-Roehr, Sean Walker

Observing Editor Diana Hannikainen

Project Coordinator Bud Sadler

Senior Contributing Editors

Robert Naeye, Roger W. Sinnott

Contributing Editors

Howard Banich, Jim Bell, Trudy Bell, John E. Bortle,

Greg Bryant, Thomas A. Dobbins, Alan Dyer,

Tom Field, Tony Flanders, Ted Forte, Sue French,

Steve Gottlieb, David Grinspoon, Shannon Hall,

Ken Hewitt-White, Johnny Horne, Bob King,

Emily Lakdawalla, Rod Mollise, James Mullaney,

Donald W. Olson, Jerry Oltion, Joe Rao, Dean Regas,

Fred Schaaf, Govert Schilling, William Sheehan,

Mike Simmons, Mathew Wedel, Alan Whitman,

Charles A. Wood

Contributing Photographers

P. K. Chen, Akira Fujii, Robert Gendler,

Babak Tafreshi

ART & DESIGN

Art Director Terri Dubé

Illustration Director Gregg Dinderman

Illustrator Leah Tiscione

ADVERTISING

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Newsstand Sales Scott T. Hill, [email protected]

4 AUGUST 2019 • SKY & TELESCOPE

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In this composite image of

the galaxy NGC 3079, X-rays

appear in pink and purple

and optical data in orange

and blue.