Phys./Geog. 182 Week 7 – Mon. - The Birth of Stars The Cone Nebula

Milky Way Photo, showing dark clouds and nebula

Interstellar matter Gas and dust Dust grains about 10-7 m in diameter, about the size of smoke particles Dust causes reddening of the light that passes through it, but NOT redshift. This is due to absorption of the blue components of light (more-so in UV).

Interstellar gas The interstellar gas is very dilute, about ONE atom per cubic centimeter. In some places it is much denser. The distribution of gas is very uneven. It is mostly Hydrogen (90%), Helium (9%), and everything else (1%).

Interstellar Clouds: A Milky Way mosaic shows dark clouds.

A third of the Milky Way Mosaic.

Another third of the Milky Way Mosaic.

Another third of the Milky Way Mosaic.

Galactic Plane, showing several nebulae. blow up this small frame

M20–M8 Region blow up this small frame

M20 (Messier 20) The Trifid Nebula

Trifid nebula, taken with ground-based telescope. Insert shows field of view of Hubble wide-field camera.

Detail of Trifid nebula, showing a pillar of cold molecular gas, & a jet coming out of a hidden star, which is about 0.5 parsec long. Blow up the upper-left corner.

Detail of Trifid nebula, showing a pillar of cold molecular gas, & a jet coming out of a hidden star, which is about 0.5 parsec long. Expand this some.

Detail of Trifid nebula, showing a pillar of cold molecular gas, & a jet coming out of a hidden star, which is about 0.5 parsec long.

Emission Nebulae Ultraviolet light causes hydrogen to glow with a pinkish color. The detail is in false colors. See the following slides for blowups of these.

M8 – The Lagoon Nebula

M8 – The Lagoon Nebula

M8 – The Lagoon Nebula – detail in false color

from the Hubble website: www.hubblesite.org

M16 - The Eagle Nebula

M16 - The Eagle Nebula, in visible light

M16 - The Eagle Nebula, in visible light - close up of pillar region.

M16 - The Eagle Nebula – the pillars in false color, from the Hubble Space Telescope. Blow up this corner, and rotate it. These are sometimes called the “Pillars of Creation”

EGGs – Evaporating Gaseous Globules These can be seen as pillars and egg-like objects.

detail of EGGs: Evaporating Gaseous Globules these can be seen as pillars and egg-like objects

finer detail of these EGGs: Evaporating Gaseous Globules

Some properties of these nebulae: note that these are AVERAGE quantities; the nebulae are actual quite uneven in their density and temperature. Note the huge masses and sizes.

Emission Nebula Spectrum

Dark Dust Clouds: Obscuration and Emission more on next slides

Dark Dust Clouds: not just an absence of stars!

Radio Emission reveals the dark dust cloud.

Dark Dust Cloud, seen in visible light.

Dark Dust Cloud revealed in infrared photo

Horsehead Nebula (neck is about 0 Horsehead Nebula (neck is about 0.25 pc across) The pink nebulae are emission nebulae.

Horsehead Nebula (neck is about 0 Horsehead Nebula (neck is about 0.25 pc across) A reflection nebula is seen to the lower left of the horsehead.

Horsehead Nebula (The neck is about 0 Horsehead Nebula (The neck is about 0.25 pc across) A nice example of a dark dust cloud

Star formation – a 7 stage process 1 – an interstellar cloud 2 – shrinking cloud fragments 3 – a fragment is the size of our solar system 4 – protostar center reaches 1,000,000 K 5 – protostar at ~10 solar radius, 4000K surf. 6 – ignition of fusion in core, now a star 7 – reaches main sequence

Atomic Motions are rarely influenced by gravity Atomic Motions are rarely influenced by gravity. They just keep colliding and coming apart. When there are enough in a cloud to equal the mass of the sun, and temperature is about 100 K, the entire cloud can start to shrink due to its own weight, and we get stage 1 of star formation. (The “collapse” of a cloud is probably “triggered” by some event in nearby space.)

Stage 2: Cloud Fragmentation probably occurs Fragments may contain one to several solar masses of molecular gas and dust.

Orion Nebula, Up Close

Orion Nebula is located in the “sword” of several objects hanging below the “belt” of Orion.

Orion Nebula, Up Close

Orion Nebula, A closer look reveals “knots” or EGGs, some of which may contain protostars.

These globules may contain evolving planets as well as the central protostar.

Several disks that may be protoplanetary disks are found after blowing up the Hubble photo.

A protostar can be plotted on the H–R diagram after reaching stage 4 A protostar can be plotted on the H–R diagram after reaching stage 4. It is heated solely due to contraction and is fairly cool, but might be 1000 times as luminous as our Sun, mostly in the infrared part of the spectrum.

Newborn Star on the H–R Diagram Stage 5 – T Tauri stage – has violent surface activity and may form “jets” Stage 6 – core at 10 million K and finally get fusion Stage 7 – reaches the main sequence

Protostellar Outflow

Protostars in Orion region top: low-mass protostar with solar-system- sized dusty disk bottom: more evolved disk around a protostar

Prestellar Evolutionary Tracks for stars of other masses The minimum mass needed to get nuclear fusion and produce a real star is about 0.08 solar mass, or about 80 times the mass of Jupiter. With less mass all we get are “brown dwarfs”

FIGURE 12-12 Pre–Main-Sequence Evolutionary Tracks This H-R diagram shows evolutionary tracks based on models of seven stars having different masses. The dashed lines indicate the stage reached after the indicated number of years of evolution. The birth line, shown in blue, is the location where each protostar stops accreting matter and becomes a pre–mainsequence star. Note that all tracks terminate on the main sequence at points that agree with the mass-luminosity relation (see Figure 11-14a).

Brown Dwarfs are “failed stars” This one has a mass of about 50 times that of Jupiter. The line is a CCD glitch

We believe that most stars form in clusters from a single large cloud that fragments. An example of an Open Cluster is the Pleiades cluster (M45, a.k.a. “the seven sisters”).

H-R diagram of the Pleiades Open Cluster