The Universe in my pocket
The realm of galaxies
Grażyna Stasińska No. 3 ES-‐001 Paris Observatory
We have all seen the large band of hazy light crossing the sky on dark nights. The ancient Greeks called it the Milky Way. For the ancient Egyptians and the ancient Chinese, it was a celestial river, while Siberians saw it as the seam in the tent of the sky. Since the oldest times scientists The Milky Way with Orion seen from Lake have tried to understand its Tahoe in Nevada (USA). nature. Many, like Anaxagoras in ancient Greece or Al Biruni in medieval Persia, considered that it was made of many stars seen close together. This idea was proven correct when Galileo Galilei observed the Milky Way with his telescope in 1610 Galileo’s drawing of the Milky Way near and showed that it was really Orion: small asterisks represent faint composed of a large number of stars. faint stars. 2 3
4 4 5 5
a small telescope by Lorenzo Comolli. Comolli. Lorenzo by telescope small a
now called galaxies. galaxies. called now
spiral galaxy. This picture was taken with with taken was picture This galaxy. spiral
the Milky Way. Such nebulae are are nebulae Such Way. Milky the
M31, the Andromeda Galaxy, the nearest nearest the Galaxy, Andromeda the M31,
’ similar to our galaxy, galaxy, our to similar ’ universes
these nebulae were in fact ` fact in were nebulae these island island
It was then shown that many of of many that shown then was It
distance to of one of them in 1924 in them of one of to distance . .
Edwin Hubble measured the the measured Hubble Edwin
Way was harshly debated until until debated harshly was Way
located inside or outside the Milky Milky the outside or inside located
Whether these clumps were were clumps these Whether
nebulae and stellar nebulae. nebulae. stellar and nebulae
that is closest to the Milky Way. Way. Milky the to closest is that
two types of nebulae: gaseous gaseous nebulae: of types two
The Large Magellanic Cloud, the galaxy galaxy the Cloud, Magellanic Large The
1863) showed that there were were there that showed 1863)
amateur astronomer Huggins in in Huggins astronomer amateur
Spectroscopy (pioneered by the the by (pioneered Spectroscopy
famous catalogue. catalogue. famous
Messier listed 104 of them in his his in them of 104 listed Messier
in the sky. In 1781, Charles Charles 1781, In sky. the in Other cloudy patches can be seen seen be can patches cloudy Other
From nebulae to galaxies galaxies to nebulae From
6 6
7 7
rocchi, with a 40 cm telescope. telescope. cm 40 a with rocchi, Qua
tt
*one hundred billion billion hundred *one This image was obtained by Keith Keith by obtained was image This
NGC 4565: a spiral galaxy seen edge-on. edge-on. seen galaxy spiral a 4565: NGC
The Milky Way is a spiral galaxy. galaxy. spiral a is Way Milky The
contain10 * stars. stars. *
11
Spiral galaxies typically typically galaxies Spiral
Large Telescope at ESO in Chile. Chile. in ESO at Telescope Large
old. old. This picture was obtained with the Very Very the with obtained was picture This
blue, and only about a million years years million a about only and blue, small companion NGC 1232A. 1232A. NGC companion small
The spiral galaxy NGC 1232 and its its and 1232 NGC galaxy spiral The while in the arms the stars are are stars the arms the in while
typically are billions of years old, old, years of billions are typically
stars are older. They are yellow and and yellow are They older. are stars
the arms and in the bulge, the the bulge, the in and arms the
stars are being formed. In between between In formed. being are stars
clouds of gas and dust where new new where dust and gas of clouds
Along the spiral arms, we we arms, spiral the Along nd nd fi
outwards from a central bulge. bulge. central a from outwards
They have spiral ‘arms spiral have They ’ that unwind unwind that ’
large galaxies in the local Universe. Universe. local the in galaxies large This is the most common type of of type common most the is This
Spiral galaxies galaxies Spiral
6 6
9 9 * ten trillion trillion ten *
without coherent rotation. rotation. coherent without and William Harris. Harris. William and
South telescope by Elizabeth Wehner Wehner Elizabeth by telescope South spirals, stars move in all directions directions all in move stars spirals,
This is an image obtained at the Gemini- the at obtained image an is This In elliptical galaxies, contrary to to contrary galaxies, elliptical In
NGC 3309. 3309. NGC
Two elliptical galaxies: NGC 3311and 3311and NGC galaxies: elliptical Two * stars. stars. * more than 10 than more
13
of a million light-years, and contain contain and light-years, million a of
elliptical galaxies have diameters diameters have galaxies elliptical
ten million stars. The largest largest The stars. million ten
Milky Way galaxy) and contain only only contain and galaxy) Way Milky
years (ten times smaller than the the than smaller times (ten years
diameters of ten thousand light- thousand ten of diameters
called ‘dwarf ellipticals’ have have ellipticals’ ‘dwarf called
The smallest elliptical galaxies, galaxies, elliptical smallest The
le gas or dust. dust. or gas le li tt
them a reddish color. They contain contain They color. reddish a them
formed of old stars which gives gives which stars old of formed
they are smooth and dim. They are are They dim. and smooth are they elongated. Unlike spiral galaxies, galaxies, spiral Unlike elongated.
Elliptical galaxies can be round or or round be can galaxies Elliptical Elliptical galaxies galaxies Elliptical
11 11 10 7479 (SBc) . . (SBc) 7479
NGC 936 (SBa), NGC 5850 (SBb) NGC NGC (SBb) 5850 NGC (SBa), 936 NGC
(Sa), NGC 1039 (Sb), NGC 628 (Sc), (Sc), 628 NGC (Sb), 1039 NGC (Sa),
tightly linked together. together. linked tightly
4270 (E7), NGC 7192 (S0), NGC 488 488 NGC (S0), 7192 NGC (E7), 4270
galaxy shapes and masses are so so are masses and shapes galaxy
NGC 1407 (E0), NGC 1052 (E3), NGC NGC (E3), 1052 NGC (E0), 1407 NGC
It is not yet fully understood why why understood fully yet not is It
photos: photos:
The tuning fork as seen with modern modern with seen as fork tuning The
decreasing galactic mass. mass. galactic decreasing
spirals – is a sequence of of sequence a is – spirals
sequence – from ellipticals to to ellipticals from – sequence
and it turns out that the Hubble Hubble the that out turns it and
measure the masses of galaxies galaxies of masses the measure
Nowadays, astronomers can can astronomers Nowadays,
remains the most popular one. one. popular most the remains
‘The Realm of Nebulae’. Nebulae’. of Realm ‘The galaxies, Hubble’s classi Hubble’s galaxies, cation cation
fi
Hubble in his 1936 book book 1936 his in Hubble
example to include irregular irregular include to example
The tuning fork diagram was drawn by by drawn was diagram fork tuning The
Even after some changes, for for changes, some after Even
shapes (see opposite page). page). opposite (see shapes
invented a way to classify their their classify to way a invented
about 400 galaxies, Edwin Hubble Hubble Edwin galaxies, 400 about After analyzing the images of of images the analyzing After
The Hubble tuning fork fork tuning Hubble The
13 13 12
Blackbird Observatory. Observatory. Blackbird
Image by J. Gabany Gabany J. by Image interacted in the past. past. the in interacted
5907. 5907.
Most galaxies have probably probably have galaxies Most
spiral galaxy NGC NGC galaxy spiral
of stars. stars. of around the edge-on edge-on the around
Faint stellar streams streams stellar Faint the formation of new generations generations new of formation the
shapes of galaxies: they stimulate stimulate they galaxies: of shapes
of NGC 6621. 6621. NGC of
Interactions change more than the the than more change Interactions
encounter has pulled a long tail out out tail long a pulled has encounter
of interacting galaxies.The galaxies.The interacting of will drag a long tail of stars. stars. of tail long a drag will
NGC 6621 and NGC 6622, a pair pair a 6622, NGC and 6621 NGC
galaxy passing near another one one another near passing galaxy
merge and form an elliptical. A A elliptical. an form and merge
ways: Colliding spiral galaxies may may galaxies spiral Colliding ways:
other may interact in di in interact may other erent erent ff
Galaxies that are close to each each to close are that Galaxies
together. together.
Universe, ellipticals tend to cluster cluster to tend ellipticals Universe,
rather isolated regions of the the of regions isolated rather
galaxy in the future. future. the in galaxy
spiral galaxies tend to be found in in found be to tend galaxies spiral
probably form a single single a form probably
Galaxies do not live alone. While While alone. live not do Galaxies
two components will will components two
interacting galaxies. The The galaxies. interacting Galaxy interactions interactions Galaxy
ESO 593-8: a pair of of pair a 593-8: ESO
overleaf
type Sa Sa type
Solutions on on Solutions An edge-on galaxy of of galaxy edge-on An
the Sombrero Sombrero the
galaxy galaxy
M 104, 104, M the meat-hook meat-hook the
NGC 2442 2442 NGC
Hamburger galaxy galaxy Hamburger
the the
a planetary nebula nebula planetary a
NGC 3628 3628 NGC
Quiz Quiz
NGC 4361 4361 NGC
an elliptical and a spiral spiral a and elliptical an
intermediate between between intermediate
a galaxy? galaxy? a
of these is not not is these of
Which one one Which
an S0 galaxy galaxy S0 an
NGC 524, 524, NGC
The Universe in my pocket No. 3 This booklet was written in 2015 by Grażyna Stasińska from Paris Observatory (France) and revised by Stan Kurtz from the UNAM Radio Astronomy Institute in Morelia (Mexico).Nr 1
Most photos were obtained with the ESO large telescopes and with the Hubble Space
Telescope. They are provided by NASA, the STScI and by ESA. The photo of the Milky Way with Orion is by Wally Pacholka (TWAN). The cover photo represents the system of interacting galaxies Arp 22; see www.annesastronomynews.com/photo- gallery-ii/galaxies-clusters/arp-227/
To learn more about this series and about the topics presented in this booklet, please visit http://www.tuimp.org
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