Sky & Telescope - July 2024 - 14

Chandra: 25 Years
More than two decades ago, Chandra found something
remarkable in the heart of the star-forming galaxy NGC
6240: not one but two supermassive black holes, separated by
3,000 light-years. These giant black holes are orbiting each
other and, given their slowly shrinking separation, might
coalesce in tens of millions of years. This future merger will
release copious amounts of electromagnetic radiation and
low-frequency gravitational waves.
Since this initial discovery, many other such supermassive
black-hole binaries have been found in multiwavelength
searches. The importance of these discoveries is profound:
They support the idea that, not only can supermassive black
holes grow through mergers, but also that there are pairs
out there converging right now. Such mergers should emit
gravitational waves, which we'll be able to observe with the
upcoming Laser Interferometer Space Antenna (LISA), set to
launch next decade.
Dwarf galaxies, too, held some black hole surprises for
astronomers. Nearly every large galaxy (including the Milky
Way) hosts a supermassive black hole in its center. But
whether black holes existed in the smallest galaxies remained
a mystery until 2011, when astronomers published Chandra
Far Out
Chandra's elliptical orbit takes it
from 9,660 kilometers (6,000 miles)
above Earth's surface out to 139,000
kilometers (86,500 miles). Even at its
closest, the X-ray telescope flies about
20 times higher than Hubble. Their
respective orbits mean that, while the
Space Shuttle could reach Hubble for
servicing, it couldn't reach Chandra.
DEPLOYMENT Commander Eileen
Collins led the deployment of the
Chandra telescope from the Space
Shuttle Columbia, captured here by
fellow astronaut Cady Coleman.
Sunshade door
Aspect camera
stray light shade
Solar array
Spacecraft
module
High Resolution
Mirror Assembly
Optical bench
Solar array
High Resolution Camera
Thrusters
Integrated Science
Instrument Module
Low gain antenna
Advanced CCD
Imaging Spectrometer
THE OBSERVATORY The Chandra spacecraft is roughly the size of a school bus. X-rays pass through the side of the telescope facing us in the
diagram; the detectors are at the rear. Solar panels provide power, while thrusters maintain the orbit around Earth.
14 JULY 2024 * SKY & TELESCOPE
DEPLOYMENT: NASA; ILLUSTRATION: NASA / CXC / J. VAUGHAN

Sky & Telescope - July 2024

Table of Contents for the Digital Edition of Sky & Telescope - July 2024

Contents
Sky & Telescope - July 2024 - Cover1
Sky & Telescope - July 2024 - Cover2
Sky & Telescope - July 2024 - 1
Sky & Telescope - July 2024 - Contents
Sky & Telescope - July 2024 - 3
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Sky & Telescope - July 2024 - Cover3
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