NGC 1700

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NGC 1700 is a large elliptical galaxy in the constellation Eridanus. It is about 120 million light-years from Earth and is around 110,000 light-years across. It was discovered by William Herschel in 1785.

What it looks like and where it came from
- Type and shape: NGC 1700 is an E4 elliptical galaxy with boxy outer edges.
- Tails and shells: It has two long tidal tails that point to the northwest and southeast, each about 165 arcseconds long (roughly 130,000 light-years at its distance). There is a faint shell near the center and chaotic dust clouds very close to the core.
- Merger origin: The tails and central shell show that NGC 1700 formed from the merger of two smaller galaxies—likely two spirals or a spiral and an elliptical. Estimates of when this merger happened vary: around 3.2 ± 1.5 billion years ago, or about 6 billion years ago.

Hot gas disk and rotation
- A disk of hot gas about 90,000 light-years across is detected in X-rays. It rotates and has a temperature of about 0.47 keV. The disk was likely created during the merger, and its cooling rate suggests the merger occurred a few billion years ago.

Globular clusters and the core
- Globular clusters: The Hubble Space Telescope found about 146 globular clusters. These clusters show two color groups: blue (old, metal-poor) and red (more metal-rich and younger). Keck Observatory data also show a large number of clusters, including red ones that are estimated to be a few billion years younger than the blue ones.
- The core: The center of NGC 1700 is younger than the rest of the galaxy (about 6 billion years old) and rotates in the opposite direction to the outer parts. This decoupled core may have formed from a separate smaller galaxy that merged with NGC 1700.

Black hole and group
- Supermassive black hole: At the center sits a massive black hole, about 425 million solar masses.
- Galaxy group: NGC 1700 is part of the LGG 123 galaxy group, along with galaxies such as NGC 1729, NGC 1741, IC 2102, and IC 399. A nearby galaxy, NGC 1699, lies a short distance away on the sky.

Distance and motion
- The galaxy’s redshift gives a heliocentric radial velocity of about 3,899 km/s. Depending on the method used, its distance is reported as roughly 117 ± 40 million light-years (about 36 ± 12 megaparsecs).