The hottest white dwarf in the Galaxy

The hottest white dwarf in the Galaxy
Diagram of the Milky Way showing our Sun, the white dwarf, and the gas cloud relative to our neighbor galaxy, the Large Magellanic Cloud (adajcent to it the Small Magellanic Cloud). The white dwarf RX J0439.8-6809 and the gas cloud are between us and the Large Magellanic Cloud. Credit: Philipp Richter/University of Potsdam

Astronomers at the Universities of Tübingen and Potsdam have identified the hottest white dwarf ever discovered in our Galaxy. With a temperature of 250,000 degrees Celsius, this dying star at the outskirts of the Milky Way has already even entered its cooling phase. The researchers also were the first to observe an intergalactic gas cloud moving towards the Milky Way - indicating that galaxies collect fresh material from deep space, which they can use to make new stars. These findings are published in the latest Astronomy & Astrophysics.

Relatively low-mass stars - like our Sun - get extremely hot towards the end of their lives. The Sun's surface temperature has been fairly constant at around 6000 degrees Celsius since its birth 4.6 billion years ago. Immediately before its source of nuclear energy is exhausted in about five billion years, the Sun will reach thirty times that temperature, going to 180,000 degrees before cooling down as a white dwarf. Computer simulations suggest that stars can become even hotter than that. The highest temperature of an observed dying star was measured to be 200,000 degrees.

The researchers' evaluation of ultraviolet spectra taken by the Hubble Space Telescope points to a new record of 250,000 degrees - a temperature which can only be reached by a star some five times more massive than our Sun. The white dwarf, RX J0439.8-6809, has already entered the cooling phase. It appears to have reached its maximum temperature of 400,000 degrees about a thousand years ago. Its chemical composition is not yet understood. Analyses show that carbon and oxygen are present on its surface - the products of the nuclear fusion of helium, a process which normally takes place deep in the core of a star.

RX J0439.8-6809 was first noticed more than 20 years ago as a very bright spot on X-ray images, indicating a source of tremendous heat. Originally it was thought to be a white dwarf carrying out nuclear fusion on its surface using hydrogen drawn from a companion star. Astronomers also assumed it was located in our neighboring galaxy, the Large Magellanic Cloud. But the new Hubble data show that the star is on the outskirts of the Milky Way, and is moving away from us at a speed of 220 kilometers per second.

The star's ultraviolet spectrum held another surprise. It indicates the presence of gas which does not belong to the star; it is part of a cloud between the Milky Way and RX J0439.8-6809. The Doppler effect enables the researchers to determine that this gas cloud is moving away from us at 150 kilometers per second and moves toward the Milky Way. Astronomers knew of the existence of gases traveling at high speed in the direction of the Large Magellanic Cloud, but were unable to tell for sure if they were in the Milky Way or in the LMC. Finding such gas in the spectrum of RX J0439.8-6809 now offers proof that the belongs to the Milky Way. But its chemical composition indicates that it originated from intergalactic space - evidence that collect fresh material from , which they can use to make .


Explore further

Hubble looks in on a galactic nursery

More information: K. Werner et al. Analysis of HST/COS spectra of the bare C–O stellar core H1504+65 and a high-velocity twin in the Galactic halo, Astronomy & Astrophysics (2015). DOI: 10.1051/0004-6361/201527261

P. Richter et al. High-velocity gas toward the LMC resides in the Milky Way halo, Astronomy & Astrophysics (2015). DOI: 10.1051/0004-6361/201527451

Journal information: Astronomy & Astrophysics

Citation: The hottest white dwarf in the Galaxy (2015, November 25) retrieved 21 September 2019 from https://phys.org/news/2015-11-hottest-white-dwarf-galaxy.html
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Nov 25, 2015
The oldest stars in the Milky Way are to be found in the halo, which is evidence that the spiral arms of our galaxy are spinning outwards. This leads me to question why Kepler's target search area is behind us, and not ahead of us, where one might expect to find more evidence of highly evolved life on exoplanets, given that life on any one of these worlds would have had more time to evolve. What is the logic behind this decision?

Nov 25, 2015
What is the logic behind this decision?


You're right - you caught 'em out! It's clearly one big conspiracy by the world's scientists to keep us in the dark about the alien lifeforms they've already discovered and communicated with.

Or, better yet, there is a lot of space to cover and, even though Kepler's currently targeting a particular area, the amount of received data to go through is already a monumental task. When they finally get around to thoroughly searching all the areas you want them to, we'll probably be dead. Anyway, I thought the actual point of Kepler was to discover exoplanets and not specifically evidence of evolved life in other systems...and do I really need to mention that this article pertains to Hubble's observations and not Kepler's?

Nov 25, 2015
"With a temperature of 250,000 degrees Celsius, this dying star at the outskirts of the Milky Way has already even entered its cooling phase."

Just on theory that presents the universe in a very strange way. The facts which can support such a claim are missing as usualy.

Nov 27, 2015
The facts are in the paper and in the 20 years of literature on this object.
So you are lying as usual.

Nov 27, 2015
The oldest stars in the Milky Way are to be found in the halo, which is evidence that the spiral arms of our galaxy are spinning outwards.

It only proves that the halo formed before the disk. How the spiral arms are moving should be evident from the doppler shift of the stars in them. Never heard that they are moving outward at any significant speed.
.

Nov 28, 2015
"The facts are in the paper and in the 20 years of literature on this object.
So you are lying as usual."

I do not care for this, because this is not scientific but emotional argument as usual from you, who are very distant from the science.

In the dark ages the 'truth" that the Earth is flat was recognized by majority and was in scientific literature for many more than 20 years. History is great teacher and it tends to repeat again and again. From it we know that the truth never was the accessible to the majority of people because of their personal choice.

Nov 28, 2015
You keep lying. Facing the truth conflicts with your delusion.
You have willfully chosen to be insane.

Nov 28, 2015
It is immoral to willfully opt for insanity.
You are a failure as a human being, viko.

Nov 28, 2015
"The facts are in the paper ...

I do not care for this ...


This is the very definition of lying: to consciously not care for the facts.

Nov 28, 2015
@viko_mx

In the dark ages the 'truth" that the Earth is flat was recognized by majority and was in scientific literature for many more than 20 years. History is great teacher and it tends to repeat again and again. From it we know that the truth never was the accessible to the majority of people because of their personal choice.


How funny that a religious nutter should spout 19th century lies invented by atheists and antitheists to foster the idea that religion holds back scientific progress. Here it's used in attempt to hold back scientific progress. There's too much [Fe] in here. I have to go get some air.

Nov 28, 2015
I do not care for this, because this is not scientific but emotional argument
@viko
you mean you don't like being outed as a liar and delusional religious fanatic... because you are the worst about "EMO" posts - like this
From it we know that the truth never was the accessible to the majority of people because of their personal choice
if you had actually READ your history, you would know that education was typical to the rich and manipulated by the church. it wasn't about choice at all.

Nov 28, 2015
Careful, CS. Viko talks religious newspeak. His words "history" and "truth" probably refer to some delusional text. He means completely different things from what most people understand by these words.

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