Sky and Telescope - March 2018 - 57

Going Deep by Al Lamperti

Ancient Photons from AGNs
Light from these faraway galaxies has traveled for millions to billions of years,
crossing vast expanses of space.
1h 50m

1h 40m

1h 30m
M74

+16°

PISCES

UGC 1195

+14°

671

677
658

+12°
683

673

Star magnitudes

660
675

5
6
7
8
9
10

t NGC 660 Situated some 43 million lightyears away, this Seyfert is a fine example of a
polar-ring galaxy. It's not yet known how these
objects came to be: One scenario postulates
the merging of two galaxies at a right angle,
while another has the host galaxy tidally stripping a passing gas-rich spiral galaxy. Only a
handful of these objects are known to date.

FR A NK COLOSIM O

f you're a deep-sky aﬁcionado who's
always looking for another challenge
to "go deep," try the Active Galactic
Nuclei (AGN) Observing Program of
the Astronomical League (https://is.gd/
al_agn). Although there are several
classes of AGNs, only three will be
addressed here: Seyfert galaxies, BL
Lacertae objects (BLL), and quasars -
see the website above for a summary of
their characteristics. In general, AGNs
are very energetic and active objects
powered by supermassive black holes,
and their complex natures can give rise
to very different outputs of radiation.
Let's take a closer look.
Seyfert galaxies are mostly spiral galaxies with less luminous AGNs, thereby
making the host galaxy visible. Many
of you have observed or imaged several
AGNs, perhaps not realizing that they

were in this category. Popular Seyfert
galaxies include M61, M81, and M104,
along with a host of Herschel objects.
There are 30 such galaxies brighter than
magnitude 13.8, and their distances are
measured in the tens to several hundred
million light-years.
BLL are hosted in massive galaxies.
Try this type of variable AGN if you
want to go deeper. They're more distant,
situated between 0.5 to 10 billion
light-years away, and as such, tend to
be dimmer, ranging in magnitude from
about 13 to 17.
Quasars are extremely bright AGNs
that overpower their host galaxy. They
are at distances listed in the millions
to billions of light-years. The brightest,
with a magnitude of 12.9, and perhaps
best known is 3C 273 in Virgo at a
distance of slightly more than 2 billion

light-years. Interestingly, Markarian
509 in Aquarius is much closer at 490
million light-years and shines at magnitude 13.1. More awe-inspiring are the
sub-types of quasars: gravitationally
lensed and double, or binary, quasars.
The former are quasars whose light has
been gravitationally distorted around a
massive foreground object and may be
split into two or more points of light
with identical spectra. The latter are
two distinct quasars in close proximity in the sky, possibly gravitationally
bound (not to be confused with the
Twin Quasar, see below) and, consequently, having different spectra.

Plan of Attack
As with any observing endeavor, preparing ahead of time will enhance the
experience. Those of you with Go To
sk yandtelescope.com * M A RCH 2 018

https://www.is.gd/al_agn https://www.is.gd/al_agn http://www.skyandtelescope.com

Sky and Telescope - March 2018

Table of Contents for the Digital Edition of Sky and Telescope - March 2018