astronomy

HE 0450−2958

HE 0450−2958 is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand HE 0450−2958 rather than just read about it. In short: HE 0450−2958 is an unusual quasar. It has been called the "naked quasar" and the "quasar without a home" because it appears to lack a host galaxy.

Key takeaways

HE 0450−2958 belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect HE 0450−2958 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HE 0450−2958 from memory before moving on to harder problems.

Reference excerpt

HE 0450−2958 is an unusual quasar. It has been called the "naked quasar" and the "quasar without a home" because it appears to lack a host galaxy. It is estimated to lie approximately one billion parsecs (3.26 billion light years) away.

History A team of researchers led by Pierre Magain of the University of Liège, Belgium announced their findings in the September 14, 2005 issue of the journal Nature. The quasar lies close in the sky to a disturbed, starburst galaxy (see figure, upper left). However, no galaxy was seen around the quasar itself (figure, middle), leading the authors to speculate

One might suggest that the host galaxy has disappeared from our view as a result of the collision [which formed the disturbed galaxy], but it is hard to imagine how the complete disruption of a galaxy could happen.

In order for the quasar's host galaxy to have escaped detection, Magain et al. estimated that it would need to be approximately five magnitudes (100 times) dimmer than expected for such a quasar, or to have a radius of 300 light-years or less (typical quasars are embedded in galaxies 5000 to 50,000 light-years across). Shortly after Magain et al.'s paper was published, three theoretical papers appeared, all in the week of November 6, 2005, which claimed to explain the peculiar properties of this object. Two of the papers—from groups in Cambridge, Massachusetts and Cambridge, England—suggested that the quasar was a supermassive black hole that had been ejected from the center of the nearby, disturbed galaxy, either by gravitational radiation recoil or by an interaction involving three black holes. The ejection velocity would have to be approximately 1000 km/s in order to place the quasar so far from its original host galaxy. The third paper, from a team led by David Merritt, critically examined the ejection hypothesis and concluded that it could not be correct. The two main arguments were: (1) The quasar spectrum reveals it to be a narrow-line Seyfert 1 galaxy. NLS1's are believed to have abnormally small black holes; since black hole size is strongly correlated with galaxy size, the host galaxy of the quasar should also be abnormally small, explaining why it had not been detected by Magain et al. (2) The quasar spectrum also reveals the presence of a classic, narrow emission line region (NLR). The gas producing the narrow lines lies roughly a thousand light-years from the black hole, and such gas could not remain bound to the black hole following a kick large enough to remove it from its host galaxy. These authors concluded that the "naked" quasar was in fact a perfectly normal, narrow-line Seyfert galaxy that happened to lie close on the sky to a disturbed galaxy.

A number of scientific studies since 2005 have supported this conclusion. (1) Kim et al. (2006) made a more careful attempt to find the quasar's host galaxy. They concluded that it was impossible to rule out the presence of a galaxy given the confusing light from the quasar. (2) Zhou et al. (2007) observed the X-ray emission from the quasar and used it to estimate the mass of the black hole. They confirmed a small mass for the black hole, implying an even fainter host galaxy than predicted by Merritt et al. (3) Feain et al. (2007) detected radio emission from the quasar, which they interpreted as indicating ongoing star formation, which "contradicts any suggestion that this is a 'naked' quasar'". The current scientific consensus is that HE 0450−2958 probably does have a host galaxy but that it is difficult to see behind the bright quasar light. Recently, the consensus has been questioned after a European Southern Observatory study. A study in 2010 discovered a "blob" of emission near the quasar. This blob is thought to be the disturbed and compact host galaxy for the quasar.

See also Dark galaxy – Hypothesized galaxy with no, or very few, stars

References

External links Black Hole in Search of a Home (ESO) Image HE 0450−2958 Black Hole Caught Zapping Galaxy into Existence? [1]

Illustrations

Worked examples

Example 1 — a first encounter with HE 0450−2958

Start with the simplest possible case. Write down what HE 0450−2958 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, 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 HE 0450−2958 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 HE 0450−2958 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 HE 0450−2958

In research: HE 0450−2958 appears in astronomy 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 HE 0450−2958 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: HE 0450−2958 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 2005, Caelum, Dark galaxies, so understanding it makes those chapters shorter.
In everyday life: Look for HE 0450−2958 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.

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How to study HE 0450−2958 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HE 0450−2958 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 HE 0450−2958 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HE 0450−2958 in simple terms?

HE 0450−2958 is an unusual quasar. It has been called the "naked quasar" and the "quasar without a home" because it appears to lack a host galaxy.

Why does HE 0450−2958 matter?

Because it connects several astronomy 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 HE 0450−2958?

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 HE 0450−2958.