The Universe in my pocket

The realm of

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 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 . 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 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. 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 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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