April 2012
Kostas Glampedakis, Ian D. Jones, Lars Samuelsson
Rotating neutron stars can become potent sources of gravitational radiation if their shape can be made non-spherical and non-axisymmetric. Such deformations (colloquially known as "mountains") can be induced by forces internal to the star, for example, by the strong stellar magnetic field.
The expected magnetic deformation is typically too small to make any known neutron star detectable by present and next generation gravitational wave detectors, however, as we have recently shown the presence of stable quark matter in neutron star interiors could be a game changer. Internal magnetic mountains induced in a "color-superconducting" quark core could make young pulsars, like the Crab and Vela, "visible" sources of gravitational waves, hence providing us with evidence of the existence of exotic matter inside these extreme objects.
Phys. Rev. Letters 109, 081103 (2012) arXiv e-print (arXiv:1204.3781)
April 2012
Sam Lander, Ian D. Jones
We only observe the exterior magnetic fields of stars; for neutron stars we can typically just infer the dipole component, from the rate at which the star's spin rate decreases. By contrast, knowing the interior field would help us understand many phenomena of neutron stars: their long-term evolution, oscillation modes and occasional dramatic flaring events. Without having direct observations, we can try to model the magnetic field inside a neutron star - a good model should be a stable equilibrium solution.
Much previous literature has assumed that a barotropic star - where the pressure is a function of density - is a good first approximation. In this case, the expectation was that a magnetic field geometry combining poloidal and toroidal components would be stable. We used numerical simulations to show that this assumption was generically wrong - the magnetic fields were unstable! Our work suggests that more advanced modelling may be crucial to finding a good model of a magnetised neutron star.
MNRAS, 424, 482 (2012) arXiv:1202.2339v1 [astro-ph.SR]
February 2012
Andrea Passamonti, Kostas Glampedakis
Non-axisymmetric oscillations in rapidly rotating neutron stars can be driven unstable by gravitational-wave radiation via the CFS instability [see A. Passamonti et al. (2013)]. The fundamental mode (f-mode) is one of the main candidates which can suffer this instability and emit a copious amount of gravitational waves.
Among the various processes which can limit the growth of the f-mode is the non-linear bulk viscosity. The non-linear terms can be activated during the instability when the mode reaches a significant amplitude.
Our results show that non-linear bulk viscosity has a moderate impact on the size of the f-mode instability window, becoming an important factor and saturating the mode’s growth at a relatively large oscillation amplitude. In addition, we show that the action of bulk viscosity can be significantly mitigated by the presence of superfluidity in neutron star matter. We show similarly that non-linear bulk viscosity leads to a rather high saturation amplitude even for the r-mode instability.
Considering an f-mode-unstable neutron star located in the Virgo cluster and assuming a mode amplitude at the level allowed by bulk viscosity, we find that the emitted gravitational wave signal could be detectable by advanced ground-based detectors such as Advanced LIGO/Virgo and the Einstein telescope.
MNRAS, 422, 3327 (2012) arXiv:1112.3931v1 [astro-ph.SR]
May 2012
Stoytcho S. Yazadjiev and Daniela D. Doneva
In modeling the neutron star interior we are forced to make certain assumptions about the properties of the neutron star matter. Some of these assumptions seem to be natural from a physical point of view, however, there are always uncertainties and suspicions that the assumptions may not be fully correct. As the science history shows there are surprises sometimes - Nature does not always share our notions for "natural". That is why the alternatives should also be investigated.
There are many alternatives to the standard neutron star models. What we considered in our work is neutron stars with anisotropic pressure and mixed neutron-dark-energy starts, i.e. stars containing both normal matter and dark energy. We study the properties of the stars and their stability. As these objects are very compact, their oscillations can produce a significant gravitational wave signal. That is why we study also the oscillation frequencies and the deviation from the standard neutron star models. Thus if gravitational waves from oscillating neutron stars are observed in the future, we can potentially determine the presence of dark energy in the compact objects, or set constraints on the anisotropy in the neutron star interior.
Phys. Rev. D 85, 124023 (2012) arXiv:1203.3963 [gr-qc]
J. Cosmology Astropart. Phys. 1203, 037 (2012) arXiv:1112.4375 [gr-qc]
Our website uses cookies. Some of them are mandatory, while others allow us to improve your user experience on our website. The settings you have made can be edited at any time.
or
Essential
in2cookiemodal-selection
Required to save the user selection of the cookie settings.
3 months
be_lastLoginProvider
Required for the TYPO3 backend login to determine the time of the last login.
3 months
be_typo_user
This cookie tells the website whether a visitor is logged into the TYPO3 backend and has the rights to manage it.
Browser session
ROUTEID
These cookies are set to always direct the user to the same server.
Browser session
fe_typo_user
Enables frontend login.
Browser session
Videos
iframeswitch
Used to show all third-party contents.
3 months
yt-player-bandaid-host
Is used to display YouTube videos.
Persistent
yt-player-bandwidth
Is used to determine the optimal video quality based on the visitor's device and network settings.
Persistent
yt-remote-connected-devices
Saves the settings of the user's video player using embedded YouTube video.
Persistent
yt-remote-device-id
Saves the settings of the user's video player using embedded YouTube video.
Persistent
yt-player-headers-readable
Collects data about visitors' interaction with the site's video content - This data is used to make the site's video content more relevant to the visitor.
Persistent
yt-player-volume
Is used to save volume preferences for YouTube videos.
Persistent
yt-player-quality
Is used to save the quality settings for YouTube videos.
Persistent
yt-remote-session-name
Saves the settings of the user's video player using embedded YouTube video.
Browser session
yt-remote-session-app
Saves the settings of the user's video player using embedded YouTube video.
Browser session
yt-remote-fast-check-period
Saves the settings of the user's video player using embedded YouTube video.
Browser session
yt-remote-cast-installed
Saves the user settings when retrieving a YouTube video integrated on other web pages
Browser session
yt-remote-cast-available
Saves user settings when retrieving integrated YouTube videos.
Browser session
ANID
Used for targeting purposes to profile the interests of website visitors in order to display relevant and personalized Google advertising.
2 years
SNID
Google Maps - Google uses these cookies to store user preferences and information when you view pages with Google Maps.
1 month
SSID
Used to store information about how you use the site and what advertisements you saw before visiting this site, and to customize advertising on Google resources by remembering your recent searches, your previous interactions with an advertiser's ads or search results, and your visits to an advertiser's site.
6 months
1P_JAR
This cookie is used to support Google's advertising services.
1 month
SAPISID
Used for targeting purposes to profile the interests of website visitors in order to display relevant and personalized Google advertising.
2 years
APISID
Used for targeting purposes to profile the interests of website visitors in order to display relevant and personalized Google advertising.
6 months
HSID
Includes encrypted entries of your Google account and last login time to protect against attacks and data theft from form entries.
2 years
SID
Used for security purposes to store digitally signed and encrypted records of a user's Google Account ID and last login time, enabling Google to authenticate users, prevent fraudulent use of login credentials, and protect user data from unauthorized parties. This may also be used for targeting purposes to display relevant and personalized advertising content.
6 months
SIDCC
This cookie stores information about user settings and information for Google Maps.
3 months
NID
The NID cookie contains a unique ID that Google uses to store your preferences and other information.
6 months
CONSENT
This cookie tracks how you use a website to show you advertisements that may be of interest to you.
18 years
__Secure-3PAPISID
This cookie is used to support Google's advertising services.
2 years
__Secure-3PSID
This cookie is used to support Google's advertising services.
6 months
__Secure-3PSIDCC
This cookie is used to support Google's advertising services.
6 months