Stars - Evolution

Andrew Conway

Stellar evolution

Star formation

The Great Orion Nebula

Orion nebula

Source: ESA/NASA Hubble Public Domain

Proplyds - Star formation in the Orion Nebula

Orion nebula - proplyds

Source: ESA/NASA Hubble Public Domain

Nuclear fusion

The p-p chain

The p-p chain

Source: Borb CC-BY SA 3.0


The Pleiades


Source: NASA, ESA, AURA/Caltech, Palomar Observatory Public Domain

Pressure vs gravity

Mass is the key

A star with larger mass will have:

Properties by mass

Mass Class Surface temperature Radius Luminosity
≥ 16 M☉ O ≥ 33,000 K ≥ 6.6 R☉ ≥ 30,000 L☉
2.1–16 M☉ B 10,000–33,000 K 1.8–6.6 R☉ 25–30,000 L☉
1.4–2.1 M☉ A 7,500–10,000 K 1.4–1.8 R☉ 5–25 L☉
1.04–1.4 M☉ F 6,000–7,500 K 1.15–1.4 R☉ 1.5–5 L☉
0.8–1.04 M☉ G 5,200–6,000 K 0.96–1.15 R☉ 0.6–1.5 L☉
0.45–0.8 M☉ K 3,700–5,200 K 0.7–0.96 R 0.08–0.6 L☉
≤ 0.45 M☉ M 2,000–3,700 K ≤ 0.7 R☉ ≤0.08 L☉

Larger luminosity, shorter lifetimes

Running out of fuel

Low mass stars

Less than two solar masses (like our Sun):

Red giant to scale

Sun as a red giant

Source: Oona Räisänen CC-BY SA 3.0

The ring nebula - a planetary nebula

The ring nebula

Source: NASA/ESA/Hubble Public Domain

Sirius B - a white dwarf

Sirius A is the brightest star in our night sky, but it has a binary companion, Sirius B, which is a white dwarf. Sirius B is the dot at the bottom left.

Sirius A and B

Source: NASA/ESA/Hubble/M. Barstow CC-BY SA 3.0

High mass stars

More than two solar masses:


Supernova 1987A

Supernova 1987A

Source: Copyright - Anglo-Australian Telescope

Supernova 1987A- aftermath

Supernova 1987A aftermath

Source: Mark McDonald CC-BY SA 3.0

1054 supernova

Crab nebula

The crab nebula

Source: NASA/ESA/Hubble Public Domain

Neutron stars


Black holes

Cygnus X-1 - artist's impression

Cygnus X-1 artist's impression

Source: ESA CC-zero

M67 - an open cluster

Open cluster M67

Source: Atlas Image courtesy of 2MASS/UMass/IPAC-Caltech/NASA/NSF Public Domain

HR diagram from M67 and NGC 188

HR diagram for M67 and NGC 188

Source: Worldtraveller CC-BY SA 3.0

Which is older?

The Sun's evolution on the HR diagram

Solar evolution on HR

Source: Lithopsian CC-BY SA 3.0