A (Very) Brief Primer on How Suns are Formed


The Milky Way is thought possibly to contain as many as 400 billion suns.

Meanwhile, Earth’s sun—a G-type main-sequence star—is believed to have formed around 4.57 billion years ago, per a Universe Today article.

Furthermore, this recent article suggests that our sun resulted from the collapse of a giant molecular cloud. Following that collapse, one fragment began to rotate. Next, its central mass became accreted. After nuclear fusion precipitated an explosion, Earth’s sun was formed.

While the Earth has only one sun, scientists have identified planets with two or more suns in their orbits.

Key Facts About Earth’s Sun

Our sun—composed of hydrogen and helium—has a diameter of 864,000 miles, as determined by NASA. While 10,000 degrees F. (or 5,538 C.) at the surface, it is far hotter—at 27 million degrees F. (or 15 million degrees C.)—internally. Furthermore, its mass is 330,000-fold that of Earth.

Similar to other yellow dwarf (G2V) stars, our Sun  is white. We just perceive it as yellow due to the effect on electromagnetic field quantums—called photons—of the our planet’s atmosphere.

However, our Sun is neither the largest nor smallest star in our galaxy. Betelgeus, Rigel, and Aldebaran are far larger, and there are billions that are smaller. Notably, 99.86 percent of the mass of our solar system is occupied by our Sun.

The Orbit of Star 51 Pegasus and its Planet

More than 1,500 planets are known to orbit other stars, per the University of IllinoisPlanet Project.

In 1995, astronomers discovered a star orbiting around a single planet in the Pegasus constellation in our galaxy. Later, this star was named Star 51 Pegasus. At 50 light-years away from Earth, Star 51 Pegasus is 1.3 times more luminous than our Sun. However, its planet entirely orbits it in only around 4.23 days.

The following are three other stars with orbiting planets:

  • HD 10180 Hydri – believed to have 6 or 7 planets (in the Milky Way; constellation, Hydrus).
  • HD 210277 Aquarii – believed to have only one planet (in the Milky Way; constellation, Aquarius).
  • 47 Urasae Majoris – believed to have 2 planets (in the Milky Way; constellation,Ursa Major).

Planets that Rotate Around Two Suns

There are planets that rotate around two suns—termed circumbinary planets. The two known planets of this type are as follows:

  • Kepler 16b (Stars: Kepler 16A and Kepler 16B) – This planet with two suns is 200 light-years distance from Earth; its two stars are 20.5 million miles apart. It was discovered in 2011, per an article in 2016 in the Astrophysical Journal.
  • Kepler-1647b – Stars: Kepler 1647A an Kepler 1647B) – 3,700 light-years distance from Earth, and its complete orbit requires 1,107 days. It was identified by astronomers at NASA Goddard Space Flight Center in 2016, per NASA website.

The Aging Process of our Sun

The Sun is predicted by scientists to begin exhausting its hydrogen in approximately 5 billion years. Consequently, it will enlarge, and its helium will eventually burn into carbon. Eventually, it will be only a dead core composed of mainly carbon and oxygen.

According to LiveScience, the dying Sun—in 7-8 billion years–will turn into a “red giant”. At that point, it will vaporize Earth. However, three “Earth-like” planets were reported in Nature that are 40 light-years away, per CNN on May 2, 2016.

Therefore, it is possible that we, humans, may be living in a different galaxy by then!