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1 Markets I: The Ecosystem and Exchange-Traded Marketsবাজার অনলাইন 2 Markets II: Rates, FX and Creditবাজার অনলাইন 3 Markets III: Commodities, Energy and Cryptoবাজার অনলাইন 4 Quantitative Methodsপদ্ধতি অনলাইন 5 Derivatives and Volatilityডেরিভেটিভস অনলাইন 6 Rates, Credit, XVA and Riskসুদহার, ঋণ ও ঝুঁকি অনলাইন 7 Research Craft: Predictors, Backtests, Measurement, Portfoliosগবেষণা অনলাইন 8 Strategies I: Equities and Futuresকৌশল অনলাইন 9 Strategies II: Volatility, Relative Value, Macro and the Bank Desksকৌশল অনলাইন 10 Microstructure and Executionএক্সিকিউশন অনলাইন 11 Market Making and High-Frequency Tradingমার্কেট মেকিং অনলাইন 12 Machine Learning for Marketsমেশিন লার্নিং অনলাইন 13 Low-Latency Softwareপ্রযুক্তি অনলাইন 14 Networks, Hardware and Trading Infrastructureপ্রযুক্তি অনলাইন 15 Research, Data and Risk Platformsপ্রযুক্তি অনলাইন 16 The Desk and the Firmপ্রতিষ্ঠান অনলাইন 17 The Industry: Firms, Roles and Careersক্যারিয়ার অনলাইন 18 Interviews I: Maths, Probability and Speedক্যারিয়ার অনলাইন 19 Interviews II: Markets, Trading Games and the Final Roundক্যারিয়ার অনলাইন 20 Interviews III: Codeক্যারিয়ার অনলাইন
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Earth and Space Sciences · পরিভাষা

Hubble sequence; elliptical, lenticular, spiral and irregular galaxies কী?

অন্য নাম: Hubble sequence · elliptical galaxy · spiral galaxy · lenticular galaxy · irregular galaxy

Definition 29.11 University Earth and Space Sciences — Year 3 · অধ্যায় 29 — The Milky Way and Galaxies

The Hubble sequence classifies galaxies by their appearance. An elliptical galaxy (type E) is a smooth system of stars, with brightness falling steadily from the centre and no disc; it is labelled Enn, with n=10(1−b/a)n = 10(1 - b/a) and b/ab/a the apparent axis ratio, from E0 (round) to E7. A spiral galaxy has a disc with spiral arms around a central bulge; it is labelled Sa, Sb, Sc in order of a decreasing bulge, more open arms and arms more broken into star-forming knots, and SBa, SBb, SBc if a bar crosses its centre. A lenticular galaxy (S0) has a disc and a bulge but no arms. An irregular galaxy (Irr, Im) has no organized structure.

The Hubble sequence drawn as a tuning fork, schematically. Ellipticals are labelled by their apparent flattening; the fork branches at the lenticulars into ordinary and barred spirals, ordered from large bulges and tightly wound arms (a) to small bulges and open arms (c); irregulars close the sequence.
The Hubble sequence drawn as a tuning fork, schematically. Ellipticals are labelled by their apparent flattening; the fork branches at the lenticulars into ordinary and barred spirals, ordered from large bulges and tightly wound arms (a) to small bulges and open arms (c); irregulars close the sequence.
The spiral galaxy M101 seen face-on by the Hubble Space Telescope, a mosaic of 51 exposures, cropped at its edges: a small, bright, yellowish bulge; open arms, bluer and knotted with clusters of young stars; brown lanes of dust along the arms. Image ESA and NASA (Hubble, heic0602), CC BY 4.0.
The spiral galaxy M101 seen face-on by the Hubble Space Telescope, a mosaic of 51 exposures, cropped at its edges: a small, bright, yellowish bulge; open arms, bluer and knotted with clusters of young stars; brown lanes of dust along the arms. Image ESA and NASA (Hubble, heic0602), CC BY 4.0.
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