With a diameter of about 60,000 light-years, the Triangulum galaxy is the third largest member of the Local Group of galaxies, roughly 60% the size of the Milky Way. It may be a gravitationally bound companion of the Andromeda Galaxy. Triangulum may be home to 40 billion stars, compared to 400 billion for the Milky Way, and 1 trillion stars for Andromeda Galaxy.

The disk of Triangulum has an estimated mass of (3–6) × 109 solar masses, while the gas component is about 3.2 × 109 solar masses. Thus the combined mass of all baryonic matter in the galaxy may be 1010 solar masses. The contribution of the dark matter component out to a radius of 55×103 ly (17 kpc) is equivalent to about 5 × 1010 solar masses.

Location

Triangulum (M33; lower left of center) and Andromeda Galaxy (M31; above center)

Estimates of the distance to the Triangulum galaxy range from 2,380×103 to 3,070×103 ly (730 to 940 kpc) (or 2.38 to 3.07 Mly), with most estimates since the year 2000 lying in the middle portion of this range,[3][4] making it slightly more distant than the Andromeda Galaxy (at 2,540,000 light-years). At least three techniques have been used to measure distances to M 33. Using the Cepheid variable method, an estimate of 2,770×103 ± 130×103 ly (849 ± 40 kpc) was achieved in 2004.[23][24] In the same year, the tip of the red-giant branch (TRGB) method was used to derive a distance estimate of 2,590×103 ± 80×103 ly (794 ± 25 kpc).

In 2006, a group of astronomers announced the discovery of an eclipsing binary star in the Triangulum Galaxy. By studying the eclipses of the stars, astronomers were able to measure their sizes. Knowing the sizes and temperatures of the stars they were able to measure the absolute magnitude of the stars. When the visual and absolute magnitudes are known, the distance to the star can be measured. The stars lie at the distance of 3,070×103 ± 240×103 ly (941 ± 74 kpc). The average of 102 distance estimates published since 1987 gives a distance modulus of 24.69, or .883 Mpc (2,878,000 light-years).[26]

The Triangulum galaxy is a source of H2O maser emission. In 2005, using observations of two water masers on opposite sides of Triangulum via the VLBA, researchers were, for the first time, able to estimate the angular rotation and proper motion of Triangulum. A velocity of 190 ± 60 km/s relative to the Milky Way was computed, which means Triangulum is moving towards Andromeda Galaxy and suggesting it may be a satellite of the larger galaxy (depending on their relative distances and margins of error). In 2004, evidence was announced of a clumpy stream of hydrogen gas linking the Andromeda Galaxy with Triangulum, suggesting that the two may have tidally interacted in the past. This discovery was confirmed in 2011. A distance of less than 300 kiloparsecs between the two supports this hypothesis.

128 minutes of amateur astrophotography directed at Triangulum Galaxy (RC10, ASI2400, EQ-6R)

The Pisces Dwarf (LGS 3), one of the small Local Group member galaxies, is located 2,022×103 ly (620 kpc) from the Sun. It is 20° from the Andromeda Galaxy and 11° from Triangulum. As LGS 3 lies at a distance of 913×103 ly (280 kpc) from both galaxies, it could be a satellite galaxy of either Andromeda or Triangulum. LGS 3 has a core radius of 483 ly (148 pc) and 2.6 × 107 solar masses.

Ha 10 x 1200s

L 53 x 300s

R 45 x 300s

G 39 x 300s

B 33 x 300s