Terzan 7 is a sparse and young

globular cluster A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of membe ...

that is believed to have originated in the

Sagittarius Dwarf Spheroidal Galaxy The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph), also known as the Sagittarius Dwarf Elliptical Galaxy (Sgr dE or Sag DEG), is an elliptical loop-shaped satellite galaxy of the Milky Way. It contains four globular clusters in ...

(Sag DEG) and is physically associated with it. It is relatively metal rich with Fe/Hydrogen.html"_;"title="Iron.html"_;"title="/nowiki> Fe/Hydrogen">H.html"_;"title="Iron">Fe/Hydrogen.html"_;"title="Iron.html"_;"title="/nowiki>Iron">Fe/Hydrogen">H">Iron">Fe/Hydrogen.html"_;"title="Iron.html"_;"title="/nowiki>Iron">Fe/Hydrogen">H=_-0.6_and_an_estimated_age_of_7.5_Byr.html" ;"title="Iron">Fe/Hydrogen">H.html" ;"title="Iron">Fe/Hydrogen.html" ;"title="Iron.html" ;"title="/nowiki>Iron">Fe/Hydrogen">H">Iron">Fe/Hydrogen.html" ;"title="Iron.html" ;"title="/nowiki>Iron">Fe/Hydrogen">H= -0.6 and an estimated age of 7.5 Byr">Gyr. Terzan 7 has low levels of nickel ([Ni/Fe] = -0.2) which supports its membership in the Sag DEG system since it has a similar chemical signature. It has a rich population of blue stragglers that are strongly concentrated toward the center of Terzan 7. It has an average luminosity distribution of M_v = -5.05. It has a half-light radius (R_h) of 6.5pc.

History

Terzan 7 was the brightest of six globulars discovered by Turkish-Armenian astronomer

Agop Terzan Agop Terzan (born Terziyan) (October 31, 1927 – April 4, 2020) was a Turkish- Armenian astronomer. Born in Constantinople Istanbul, he finished his high school from Getronagan Armenian High School, after he received his Bachelor's Degree in Ma ...

in 1968.

Young globular

Nearly all globular clusters of the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

galactic halo A galactic halo is an extended, roughly spherical component of a galaxy which extends beyond the main, visible component. Several distinct components of galaxies comprise the halo: * the stellar halo * the galactic corona (hot gas, i.e. a plas ...

formed at the same time (12-15 Gyr). Even the far situated

NGC 2419 NGC 2419 (also known as Caldwell 25) is a globular cluster in the constellation Lynx. It was discovered by William Herschel on December 31, 1788. NGC 2419 is at a distance of about 300,000 light years from the Solar System and at the same dista ...

(~100 kpc from galactic center) has a similar age. This trend also applies to the age of globulars found in the Large Magellanic Cloud and Fornax Dwarf (~140 kpc from galactic center). However, a few globulars seem to be significantly younger than the rest; these include

Palomar 1 Palomar 1 is a globular cluster part of the Palomar group in the constellation Cepheus in the halo possibly in the Outer Arm of the Milky Way galaxy. First discovered by George O. Abell in 1954 on the Palomar Survey Sky plates, it was catalo ...

, Palomar 3, Palomar 4, Palomar 12, Palomar 14, Ruprecht 106, IC 4499, Arp 2, Eridanus, Fornax 4, and Terzan 7. In particular, the ones associated with the Sag DEG appear to have formed more recently. The data suggests that all the present outer halo globulars may have originally formed in dwarf spheroidals.

Hierarchical galaxy formation

Alternatively, a hierarchical galaxy formation model is hypothesized under which a portion, possibly large, of the Milky Way's globular clusters would have originated in the accretion of other dwarf spheroidals like Sag DEG. The best candidate for this idea is Palomar 12.

Notes

75.7 kly × tan( 7′.3 / 2 ) = 160 ly. radius

References

{{DEFAULTSORT:Terzan 07 Globular clusters Sagittarius Dwarf Spheroidal Galaxy Sagittarius (constellation) ?