What happens if a star is even hotter than blue Sirius? In such cases Planck's law still applies, but the resulting glow will be of a color beyond the range to which our eyes or ordinary telescopes are sensitive. In particular, objects much hotter than Sirius will glow in ultraviolet or X-ray light. Different temperatures, and their connection to color through the law of black body radiation, reveal that seemingly distinct phenomena such as ultraviolet light and X-rays are really just parts of the broad electromagnetic spectrum. The electromagnetic spectrum describes a whole range of different colors, well beyond the sliver of light that we can see with our eyes.
So white dwarfs are buried deep within their planetary nebulas, and are so hot that they don't emit much visible light, but instead radiate mainly in the ultraviolet and X-ray parts of the spectrum. It's thus not too surprising that the superheated star at the center of the Red Spider Nebula remained unseen for many decades. That situation finally ended in 2005, when Mikako Matsuura and colleagues used the powerful Hubble Space Telescope, located in orbit above the Earth's atmosphere, to identify a tiny speck of light corresponding to the white dwarf at the heart of the Red Spider. In this and subsequent studies, astronomers have been able to make a precision measurement of the star’s color, and then have used Planck's law of black body radiation to calculate its temperature.
The results are astonishing—the surface temperature of the star at the center of the Red Spider Nebula is an incredible 540,000 degrees F, more than 50 times hotter than the Sun, and 30 times hotter than mighty Sirius.
This amazing star, with its extreme temperature and the spectacular glowing nebula that surrounds it, is of more than mere academic interest. For in gazing at the Red Spider, we are seeing our future fate. Around 5 billion years from now, the Sun too will run out of fuel, and will similarly shed its outer layers. All that will remain of our star and its solar system will be a beautiful planetary nebula, illuminated by an intensely hot white dwarf at its center.
Reprinted from Extreme Cosmos by Bryan Gaensler by arrangement with Perigee, a member of Penguin Group (USA) Inc., Copyright (c) 2011 by Bryan Gaensler.
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Reply | Report Abuse | Link to thishttp://www.eurekalert.org/pub_releases/2012-07/e-tbs072412.php
Planck's law is misleadingly explained.
Reply | Report Abuse | Link to thisWhen an object heats up, the PERCENTAGE of light get higher for shorter wavelengths.
However, the absolute amount of light increases at EVERY wavelength, ust more slowly at long wavelengths; so there's plenty of visible light coming from a white dwarf.
Therefore, it's the other two reasons mentioned that make the star difficult to see: it's small, and it's obscured.
This article states:
Reply | Report Abuse | Link to this"...the real action is happening deep within a star's core, where the fury of nuclear fusion generates all a star's heat and light for up to billions of years. But when a typical star finally exhausts all its fuel, it puffs off most of its outer layers into a slowly expanding shell of gas, exposing the central core. This core, a small dense ball of helium, carbon, and heavier elements, is no longer burning any gas via nuclear fusion, but is still incredibly hot. This dying ember, known as a “white dwarf," is now among the hottest stars in the Universe..."
However, as stated by
http://en.wikipedia.org/wiki/White_dwarf
"A white dwarf is very hot when it is formed, but since it has no source of energy, it will gradually radiate away its energy and cool down. This means that its radiation, which initially has a high color temperature, will lessen and redden with time. Over a very long time, a white dwarf will cool to temperatures at which it will no longer emit significant heat or light, and it will become a cold black dwarf. However, since no white dwarf can be older than the age of the Universe (approximately 13.7 billion years), even the oldest white dwarfs still radiate at temperatures of a few thousand kelvins, and no black dwarfs are thought to exist yet."
Doesn't this imply that most of the discussion about which is the hottest star referring to surface temperature? If I understand correctly, the cores of many stars producing fusion reactions within their cores may be hotter than the surface of a white dwarf, which has generally concluded its fusion processes, but since their heat and light must pass through their outer layers the surface of newly formed white dwarfs appear to radiate more heat.
This is an excerpt from a book, so I guess that the terminology used reflects that for it's target audience…? But it always seems weird to me to see temperatures quoted in degrees Fahrenheit for scientific items.
Reply | Report Abuse | Link to this– although degrees Kelvin are mentioned in the comments.
540,000 degrees F is clearly exceptionally hot…
But would be more informative expressed in degrees K or degrees C
(After calculating, I got the answer 300,000 K - )
Same issue with Pounds and Miles…
- don't really belong even in 'popular science'…
QBitSci
Reply | Report Abuse | Link to thisYes, we live in a digital world but ship speed is still measured in 'knots' - ocean distances are measured in 'nautical miles' - tide charts are measured in 'fathoms' - Mt Everest is still described in 'feet' - eggs are sold by the 'dozen' - cattle are penned in 'yards' - auto tyres and rims are measured in 'inches' - tyre pressure is measured in 'PSI's' (pounds per sq. Inch.)the most expensive (and arguably best) watches in the world are 'analogue'...
I can live with that. I get your point tho'.
BMR
Why don't you use more scientific units, such as the SI unit, or use Km instead of mile, use Celsius (C and Kelvin temperatures are nearly the same at high temperatures) instead of F, in scientific artical?
Reply | Report Abuse | Link to thisIs this article a scientific article?
I prefer the use of F rather than C (for temperatures only!) because:
Reply | Report Abuse | Link to this1. I grew up with it and am comfortable with the scale.
2. It better intimates ambient temperatures for human consumption because the scale is broader (32-212 versus 0-100).
3. There is no scientific reason to only count in tens.
"Its surface temperature of 9,900 degrees F results in a yellowish light, just as Planck's equations predict."
Reply | Report Abuse | Link to thisWait a minute! It isn't as though this prove Planck's equations. Do we have any other means to measure temperature of a star? Isn't it more that see the color, which tells us the temperature?
I agree that these figures should be in SI, each with English equivlent and maybe with a conversion factor. More of us might come see the lack of common sense of other systems.
Reply | Report Abuse | Link to thisHi,
Reply | Report Abuse | Link to thisYes, there are sophisticated ways to measure the temperature of a star, way beyond the scope of this short article. A detailed spectrum of the star's light allows one to assign a spectral and luminosity class to the star, based on the presence and absence of emission and absorption lines. These are compared to standard templates generated from sophisticated simulations to accurately determine the star's temperature.
The article you're reading is an extract from my book, "Extreme Cosmos". The originally published version of the book was for Australia and New Zealand, and is full of appropriate SI units (kilometres, kilograms, etc.). However, when the book was republished in the US, the publisher made the decision to convert all the numbers to imperial units (miles, pounds, etc.). This extract is taken from the US edition, hence the US units used throughout.
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