This power point presentation is helpful for astrophysicist whose are interested about magnetic field,mass,rotational curve and luminosity of our galaxy.In this slide,there are some very interesting graph and a video clip which is helpful for imagination.

1. Almighty is Great
MD:SIRAJ UD DAULA SHAMIM
DEPARTMENT OF PHYSICS
JAHANGIRNAGAR UNIVERSITY
Welcome to my
Presentation

2. Contents
 Mass of milky way galaxy
 Luminosity distribution of galaxy
 Magnetic field of our galaxy
 Rotational curve of galaxy

3. Mass of the Milky Way Galaxy
There are multiple ways of determining the
mass of a galaxy:
 By Luminosity: One way is to measure the luminosity of the
entire galaxy , then determine the mass of the galaxy. This
method can’t measure the mass of invisible matter, like Black
Holes.
 By Gravity: Another way is to use gravity to measure mass,
since all the matter in the universe is expected to interact
gravitationally. Using this method, we should be able to measure
the mass of objects even if they are invisible to our eyes by their
effects on nearby objects.

4. Luminosity Distribution of Galaxies
In astronomy, luminosity is the total amount of energy emitted by a star, galaxy,
or other astronomical object per unit time.
In 1930 ,Hubble investigated the luminosity distribution in elliptical galaxies and
expressed the distribution law as,
I(r) =
𝐼0
( 1+
𝑟
𝑎
)2
Where,
𝐼0 refers to the central intensity
and a is the solar constant.
 The luminosity of the Milky Way galaxy according to this is 5×10^36 Watts .

5.  In general the mass luminosity
ratio is assumed to be constant
for any particular galaxy , in
order to determine the mass
distribution from the observed
luminosity distribution.
 For stars on the main
sequence, luminosity is also
related to mass:
L⊙ = solar luminosity
Hertzsprung –Russell diagram
Mass-Luminosity Relation

6. Luminosity and Mass vs Distance
 The visible light from stars we
observe suggests that the
majority of the mass of the
Milky Way should be
concentrated near the center.
 Looks bright at center so most
the mass should be at the center.
Distance from the Galactic Center
Lightfromstars
Distance from the Galactic Center
Mass

7. Estimates of the mass of the Milky Way vary, depending upon the method
and data used.
Avarage the mass of the Milky Way is 5.8×1011 solar masses (M☉),
The total mass of all the stars in the Milky Way is estimated to be between
4.6×1010 M☉ and 6.43×1010 M☉.
In addition to the stars, there is also interstellar gas, comprising 90%
hydrogen and 10% helium by mass,
 The mass of this gas is equal to between 10% and 15% of the total mass of
the galaxy's stars.
 Interstellar dust accounts for an additional 1% of the total mass of the gas.
Mass of the Milky Way Galaxy

8. Magnetic Field
of Milky Way Galaxy

9. Magnetic Field of Milky Way Galaxy
 The main magnetic field structure lies in the plane of
the disc and follows the spiral arm.
.
 The arrows indicate the direction of the magnetic field,
assumed to lie along spiral arms.
The axisymmetric model derived from polarization
surveys and rotation measures of extragalactic sources
 The red arrows are in the opposite direction to the
black ones i.e the magnetic fields is reverse.

10. The bisymmetric model of the large-scale structure of
magnetic fields in the Milky Way disk, derived from pulsar
rotationmeasure
 The arrows indicate the direction of the magnetic field,
assumed to lie along spiral arms.
 The locations of the Sun and the Galactic Center (GC)
are indicated on the model.

11. Rotation Curve of the
Milky Way Galaxy

12. Solid Body Rotation Curve
Example: Merry-Go-Rounds
• Every part of the merry-go-round
“orbits” the center in the same
amount of time
– Inner part moves slow
– Outer part moves fast
Merry-Go-Rounds

13. Keplerian Rotation Curve
Example: Our Solar System
The period of each planet depends on its distance from the Sun
– Kepler’s 3rd Law: P2 ∝ a3
– Planets farther away form the sun go much slower.

14. The Milky Way Galaxy’s
Rotation Curve
The rotation curve
of a disc galaxy
(also called a
velocity curve) is a
plot of the orbital
speeds of visible
stars or gas in that
galaxy versus their
radial distance from
that galaxy's centre.

15. However the flat
rotation curve tells
a different story?
 Because there is a flat
rotation curve there should
be an equal amount of mass
distributed everywhere
throughout the galaxy’s
disk and halo.
Distance from the Galactic CenterMass
Mass curve
determined
from Light
Mass curve
determined from
the rotation
curve

16. So which mass
curve is right?
The mass curve determined from
the rotation curve is our current
best model for how the mass of the
galaxy is distributed. Mass evenly
distributed everywhere in the disk
and halo.
But that is a problem. Where is all
the missing mass and why can’t we
see it? Distance from the Galactic Center
AmountofMass
Mass curve
determined
from Light
Mass curve
determined from
the rotation
curve

17. Where is the missing Mass?
Dark matter – massive objects (matter)
that are (is) distributed evenly around the
galaxy in both the halo and disk.

18. Dark Matter
• All galaxies exhibit the same
problem of “missing” matter
• Dark Matter
• Does not emit light
• Not mysterious or evil matter,
just not seen
• Possibilities:
Brown Dwarfs, Neutrinos, Black
holes, MACHOS, WIMPS
We can not see 70-90% of the matter that makes up our Galaxy!!
Vera Rubin
Discoverer of Dark Matter

19. Comparison

20. That’s all,
Thanks everyone for
attention.