Is nebula bigger than galaxy
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Comparing the Size of Nebulae and Galaxies
Introduction to Nebulae and Galaxies
Nebulae and galaxies are two of the most fascinating structures in the universe. Nebulae are vast clouds of gas and dust, often serving as the birthplaces of stars. Galaxies, on the other hand, are massive systems composed of stars, stellar remnants, interstellar gas, dust, and dark matter, bound together by gravity. Understanding the relative sizes of these structures can provide insights into the scale and complexity of the universe.
Size of Nebulae
Enormous Lyα Nebulae
Enormous Lyα nebulae (ELANe) are some of the largest known nebulae, often associated with regions of high galaxy density. These nebulae can extend over hundreds of kiloparsecs (kpc). For instance, the "Slug" and "Jackpot" nebulae have been observed to extend over 300-500 kpc around quasars. Another study discovered an ELAN with an end-to-end spatial extent of 442 kpc, making it one of the largest known nebulae.
Planetary Nebulae
Planetary nebulae, which are the remnants of dying stars, are much smaller in comparison. They typically span a few light-years across. For example, the planetary nebulae in the Local Group galaxies such as IC 10, Leo A, and Sextans A are confined to much smaller regions, with the optical size of IC 10 being around 3.6 kpc × 2.7 kpc.
Size of Galaxies
Milky Way and Andromeda
Galaxies are significantly larger than most nebulae. The Milky Way galaxy, for instance, has a halo extending up to 136 kpc. The Andromeda galaxy (M31), another massive galaxy in the Local Group, has a halo with a mass of approximately 12.3 × 10^11 solar masses and a scale length of about 90 kpc.
Galaxy Clusters and Overdensities
In regions of high galaxy density, such as those traced by Lyα nebulae, galaxies can be found in close proximity. For example, a study of Lyα nebulae at z ≈ 2.3 found that galaxies within 320 proper kpc of a Lyα nebula are significantly brighter and more massive than those in the field. Another study discovered a quadruple quasar system embedded in a giant nebula, suggesting the presence of a massive galaxy cluster.
Conclusion
In summary, while some nebulae, particularly the enormous Lyα nebulae, can reach impressive sizes of several hundred kiloparsecs, they are generally smaller than galaxies. Galaxies, especially those like the Milky Way and Andromeda, have halos extending up to hundreds of kiloparsecs and contain vast amounts of mass and numerous stellar systems. Therefore, on average, galaxies are larger than nebulae, although the largest nebulae can approach the size of smaller galaxies.
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