Hydra A

Key takeaways

Hydra A belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Hydra A to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Hydra A from memory before moving on to harder problems.

Reference excerpt

Hydra A (also known as 3C 218), is a giant elliptical galaxy with an active galactic nucleus and has a redshift of (z) 0.054. Since its designation as Hydra A, the galaxy is located in the constellation of Hydra at a distance of 840 million light-years according to redshift values. It was discovered in 1952 by the Australian astronomer Bernard Mills during a survey of strong radio sources. Hydra A is one of the brightest X-ray sources in the sky as seen from Earth. It is also categorized as a Type-cD galaxy.

Observation Hydra A is located in a galaxy cluster named ClG 0915.7-1153 containing six galaxies. According to the redshift values of the different galaxies measured by the NOAO Fundamental Plane Survey and the X-ray distance measurement by the ROSAT X-ray space telescope, the cluster ClG 0915.7-1153 is located at 742 million light-years. According to studies, the cluster is said to be part of another galaxy cluster called Abell 780, with Hydra A likely dominating the optical center. A secondary nucleus is suggested to be located around 14 kiloparsecs away from the primary nucleus with an angle orientation of 125°.

In 2009, a Chandra X-ray Observatory study of Hydra A revealed the first images showing that Hydra A's central black hole experienced a very violent eruption that propelled iron-rich gas in the form of an extremely hot jet of matter with a temperature of 10 million K. Evidence of powerful explosions from the supermassive black hole at the galaxy's center is visible in the data from Chandra in X-ray and in the radio emission jets observed by the Very Large Array and in optical wavelength from the Canada-France-Hawaii Telescope and the Digitized Sky Survey show galaxies in the cluster ClG 0915.7-1153. An analysis of the Chandra data shows that the gas along the direction of the radio jets is enriched in iron and other metals. It is believed these elements were produced by a Type Ia supernova explosions in a large galaxy at the center of the cluster. A powerful explosion from the supermassive black hole then pushed the material outward, over distances spanning nearly 400,000 light-years. About 10 to 20 percent of the galaxy's iron was displaced, requiring a few percent of the total energy produced by the central black hole. The explosions from the central supermassive black hole not only pushed elements outward but also created a series of cavities in the hot gas. As these jets traveled through the galaxy in the surrounding multi-million-degree intergalactic gas, they pushed the hot gas aside to create the cavities. A relatively recent explosion created a pair of cavities visible as dark regions in the Chandra X-ray Observatory image surrounding the radio emission (in red). These cavities are so large they could contain the entire Milky Way, but they are dwarfed by even larger cavities, too faint to be seen in this image created by older, more powerful explosions of the black hole. The larger of these cavities is immense, spanning about 670,000 light-years. In several respects, this case resembles that of NeVe 1, MS 0735.6+7421 and RX J1532.9+3021.

Central black hole mass

Thanks to data recorded by the CXO and the VLA, the mass of the black hole could be estimated. Based on X-ray and radio emissions, as well as the speed and heat of the jets, the black hole's mass is estimated at 900,000,000 solar masses (M☉; 1.8×1039 kg), making it 200 times more massive than the Milky Way's supermassive black hole, also known as Sagittarius A*. A team of five American astronomers working with CXO data estimated that the black hole erupted approximately 2 to 5 million years ago, with the two jets having an estimated power of 1×1061 ergs (1×1054 J). The black hole is thought to have propelled matter in the form of a jet over a distance of 300,000 parsecs (980,000 ly) and the matter would have cooled over a distance of 100,000 parsecs (330,000 ly) before the jet stopped. The black hole eruption would have been caused by the fall of an immense amount of matter into the black hole, which would have absorbed more than 0.25 to 0.1 M☉ per year. This configuration results in a black hole of 10 billion M☉, much larger than previously estimated. X- ray and radio measurements show that the center would be surrounded by a disk of cold gas expelled by the black hole. A comparison of the X-ray emission and the Eddington ratio allowed calculations of the mass of the central black hole. According to the calculations, such an eruption implies a black hole with a mass of 4 billion M☉.

References

External links

Hydra A on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

Illustrations

Worked examples

Example 1 — a first encounter with Hydra A

Start with the simplest possible case. Write down what Hydra A claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Hydra A before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Hydra A ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Hydra A

In research: Hydra A appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Hydra A in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Hydra A is common in secondary-school and first-year university syllabi. It links to neighbouring topics Hydra (constellation), so understanding it makes those chapters shorter.
In everyday life: Look for Hydra A outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Hydra A in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Hydra A means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Hydra A out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Hydra A in simple terms?

Hydra A (also known as 3C 218), is a giant elliptical galaxy with an active galactic nucleus and has a redshift of (z) 0.054. Since its designation as Hydra A, the galaxy is located in the constellation of Hydra at a distance of 840 million light-years according to redshift values.

Why does Hydra A matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Hydra A?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Hydra A.